It’s pretty meta that I’m sitting with an actress who’s the epitome of Upper East Side sophistication in a hotel that’s the epitome of Upper East Side sophistication.

But then, some Wednesdays are better than others.

Christine Baranski showed up for lunch at the Mark looking like a million bucks, wearing a belted black Michael Kors pantsuit and blue-tinted Robert Marc sunglasses, every hair of her highlighted bob in place, her makeup perfect. In fact, she looked exactly like the prototypical New York society woman drawn on the hotel’s coasters, except without the designer dog tucked under her arm.

At 70, Ms. Baranski is busier than ever. She has wrapped up the sixth and final season of Robert and Michelle King’s “The Good Fight,” a spinoff of “The Good Wife.” The show has continued the adventures of the liberal Chicago lawyer Diane Lockhart, now working at a prestigious, predominantly Black law firm. But “The Good Fight” has a more madcap feel — as if everyone’s about to break out in song — blending fantasy and current events with fun guest stars playing real luminaries or thinly veiled ones. Diane becomes a conspiring leader of the Resistance against Donald J. Trump.

The beginning of the end starts streaming this Thursday on Paramount+. She is also filming the second season of Julian Fellowes’s frock opera “The Gilded Age.” And on her breaks from TV, she has been studying T.E. Lawrence and Oscar Wilde at Oxford University.

Now her biggest ambition, she jokes, is to play the Fool to Meryl Streep’s Lear.

She could do it. She has theater chops and went to Juilliard in a golden era that produced Robin Williams, Patti LuPone, Kevin Kline and Mandy Patinkin.

“I wasn’t movie-star beautiful,” she said, “which is probably why I didn’t aspire to be a film actress.”

But she became a TV star in her 40s and wowed fans with her comedy skills in movies like “The Birdcage,” “Bowfinger” and “Mamma Mia!” (not to mention Broadway’s farcical “Boeing-Boeing”).

Ms. Baranski is a throwback to those 1940s actresses like Rosalind Russell and Eve Arden who could be campy and glamorous, cutting and moving, wicked and loyal, all at the same time. In other words, the perfect best friend.

‘She Has a Little Elaine Stritch in Her’

“I live on the Upper East Side, but I don’t usually look like this,” she said apologetically, explaining that she had just come from “fluffing and glossing” for The Times’s photo shoot.

I don’t believe her, of course. Her co-stars have already told me that she is enviably meticulous.

“We’d be flying to the Emmys, and I’d look over and she’d be there, lipstick perfect, those long legs, crowned with that gorgeous mop of hair, reading The New York Times,” said Julianna Margulies, who starred with Ms. Baranski in “The Good Wife.”

Cynthia Nixon plays Ms. Baranski’s younger, meeker sister in “The Gilded Age,” and nearly 39 years ago, she played her teenage daughter in the original Broadway production of Tom Stoppard’s “The Real Thing,” directed by Mike Nichols. (Ms. Baranski won a Tony for that role.)

“She’s a little girl from Buffalo, but she always seems like she dropped in from Paris,” Ms. Nixon said. “She’s such a citizen of the world. She never stops cultivating her garden, whether she’s reading, researching, working on her instrument — that amazing body.”

Meryl Streep, who appeared with Ms. Baranski in two “Mamma Mia!” movies, chimed in about her 5-foot-10 friend: “Her posture is like a queen.”

Ms. Baranski said merely, “I do Pilates and I’m moderate in my habits. I have good genes.”

As someone who’s perennially messy, I’m fascinated by women who never leave the house looking less than perfect, as if they just pulled everything they’re wearing from a tissue-laden box. (My sister is like that.)

I leaned over to examine Ms. Baranski more carefully and figure out how she does it. But I knocked over the pitcher of half-and-half for her coffee, which spilled all over her side of the table and dripped toward her black suit. Without missing a beat, she covered the mess with a napkin and kept talking about Tom Stoppard.

She is also the type who would never miss a performance or show up not knowing her lines. Once, before she opened at the Kennedy Center in Washington in the title role of the musical “Mame,” she slipped and fell on a New York sidewalk and broke her right kneecap. (She jokingly renamed the show “Maimed.”) But by opening night two months later, she still managed to dance and sweep up and down the grand staircase.

Not to say that the actress is as starchy as Agnes van Rhijn, her character in “The Gilded Age,” a fearsome figure who, not unlike Maggie Smith’s Dowager Countess in “Downton Abbey,” can level you with one put-down or averted gaze. That’s a type that Julian Fellowes, the creator of both shows, calls “sardonic old survivors,” matriarchs trying to hold up the slipping standards of society.

Unlike Aunt Agnes, Ms. Baranski has been known to have nude swimming parties in the moonlight at her lake house in Connecticut with fellow actors like Mark Rylance and Cherry Jones.

“There is indeed lovely bacchanalian behavior, but nothing untoward,” she said. “I think Cherry in particular just doesn’t care if she swims naked in the day or the night.”

“Christine exudes class and grace, but she can throw back a martini, eat a hot dog and talk sports with the best of them,” Ms. Margulies said.

Ms. Baranski is an opera aficionado and a devout Buffalo Bills fan, with a T-shirt that says “Buffalo, a drinking town with a football problem.” And as for her martinis, she said, she likes Grey Goose with a twist — and vermouth just as “an afterthought.” She stops at one and a half, unable to keep up with her character in the 1990s sitcom “Cybill,” Maryann Thorpe, who was fabulously dressed, politically incorrect and never without her favorite accessory: a martini.

A typical conversation between Cybill and Maryann:

Cybill: “You know what is amazing, Maryann?”

Maryann: “They make vodka from wheat!”

Although the two women had great on-air chemistry, Cybill Shepherd — on whom the show was based — addressed off-air tensions in her memoir, writing that she found Ms. Baranski standoffish. People connected to the show told me that the fact that Ms. Baranski won an Emmy for her role and Ms. Shepherd did not contributed to the tensions, and Ms. Shepherd wrote, “the grain of truth in this controversy was that of course I was envious. Who doesn’t want to win an Emmy?”

Tom Werner, one of the show’s producers, brushed off the criticism of Ms. Baranski. “She wasn’t snobby,” he told me. “She was brilliant.”

Ms. Baranski said, “Can you believe that still comes up? People still want to know.” She declined to discuss Ms. Shepherd further.

Maryann was so popular that Ms. Baranski shied away from tippling roles afterward, for fear of getting typecast.

“When I’m asked to pose for pictures,” she said, “I never pose with a drink in my hand.”

Michael Kahn, who taught Ms. Baranski acting at Juilliard, gave her high praise, saying, “She plays somebody who’s tipsy better than anyone I know.” It’s easier for women to be funny acting drunk than men, Ms. Baranski said.

“She has a little Elaine Stritch in her,” said Ms. Streep, whose oldest daughter, Mamie Gummer, worked with Ms. Baranski in “The Good Fight” and whose youngest daughter, Louisa Jacobson, plays the ingénue in “The Gilded Age.” (Ms. Streep had to break the news to Ms. Baranski that Ms. Jacobson is “terrified” of her when she’s in character as Aunt Agnes.)

Ms. Margulies recalled that once, when she and Ms. Baranski were walking to see a Costume Institute exhibition at the Metropolitan Museum of Art, they were accosted by a gang of autograph seekers.

Ms. Baranski drew herself up to her full height, surveyed the group, told the ringleader with asperity, “Oh, no, darling, don’t be silly,” and kept walking.

‘Twelfth Night’ and Witchy Baths

Ms. Baranski’s grandparents were immigrants who had been stage actors in their native Poland. She grew up in a blue-collar Polish American neighborhood in a suburb of Buffalo. Her father, who died when she was 8, edited a Polish-language newspaper, and her mother had a job ordering parts for air-conditioning factories.

Ms. Baranski went to a Catholic girls’ school, and we swapped stories about scary nuns. In high school, she adopted a grander way of speaking, akin to Madonna’s odd English accent.

“I think I decided I didn’t want to sound like a Buffalo girl,” she recalled, “and people would ask me, ‘Are you English?’ I’d say, ‘No, I’m just affected.’”

She had trouble with the sibilant “S” and was rejected from Juilliard when she first auditioned. After she capped her two front teeth — “I had a gap like Lauren Hutton’s, but not as beautiful” — and took speech lessons, the drama school let her audition again, with a page full of S’s. She did a speech of Viola’s from “Twelfth Night,” but mispronounced Viola.

“It’s Vy-ola,” a judge on the faculty boomed. “Vee-ola is the instrument. Wrong department.”

Ms. Baranski joked that she was admitted “by the skin of my teeth.”

Then, maybe just to show them, she won acclaim starring in a cascade of “S” productions: Shakespeare, Stoppard, Sondheim, Neil Simon, Cybill Shepherd and “The Simpsons.”

She was married for 30 years to the actor Matthew Cowles, until his death in 2014. He had a long recurring role on “All My Children” as Billy Clyde Tuggle.

“He was a white-trash pimp and he wrote his own material,” Ms. Baranski said. “They took him off the air for a while because Jerry Falwell and the Moral Majority were cleaning up television and he had to go.”

She once did a guest appearance with him. “Ten days after having my firstborn, we agreed to be on a plotline where I was Billy Clyde’s white-trash girlfriend living in a trailer park,” she said. “He and I kidnapped one of the leading characters. Please promise me you won’t look it up. It’s so bad that it’s kind of great.”

She gave her husband credit for handling it well when she gained more star wattage.

“It was so hard,” she said, her voice wavering. “I was on the red carpet at an Emmy event and we were standing together and a photographer shouted out: ‘Get out of the way. You’re standing in her light.’ And he did.

“He was such a bighearted man. He was really happy for me and proud of me.”

They had two daughters: Isabel, who has a law degree and is a writer, and Lily, an actress who just produced her own film, a surreal short about a woman who loses her teeth, one by one.

Her friends rave about Ms. Baranski’s dedication as a mother, noting she flew back on a red eye from Los Angeles to Connecticut every weekend when she was filming “Cybill.” And they are amazed at the flair she puts into being a grandmother to three boys.

Ms. King, the “Good Fight” co-creator, marveled at how Ms. Baranski would not simply bathe her grandchildren: “She bathes them outdoors and pretends to be a witch and throws a cauldron of water on them and cackles.”

“I’m a terrifying, wonderful witch,” the actress said brightly. “My mission is to keep them away from screens because when we raised our girls in Connecticut, there was no TV in the house. I know children can have happy childhoods without being mesmerized and stupefied by screens.” (Maybe she’s drawing from her own admitted overdosing on MSNBC in the Trump era.)

Ms. King said that Ms. Baranski was also nurturing to the crew. “If somebody needs help, she is just going to quietly give it,” she said, adding that when one crew member was injured and couldn’t work for months, Ms. Baranski was one of the people who gave him money “so he could continue to have food on the table.”

‘Thank God for Pilates and Talcum Powder’

When “The Good Fight” began, the Kings assumed that Hillary Clinton would be president. In the middle of filming the pilot, they had to retool. The show began with an opening shot of Diane Lockhart, in a black dress and pearls, with her mouth hanging open, watching Mr. Trump’s inauguration. Now Diane is contending with the jaw-dropping idea that he may be announcing another run for president (if he’s not in jail).

“Six years later, can you believe that this guy is still in our brains, taking up all this real estate?” Ms. Baranski said, biting into a cookie. She blames the news media in large part. “Everything he said was covered, every outrageous thing,” she said. “It gave him so much traction.”

The show wades into thorny racial issues, depicting a power struggle between Diane and Black partners who do not want her at the top of the firm because of her race.

The Kings were so impressed with Ms. Baranski’s ability to be sexy throughout her 60s that, for the final season, they put her character in a romantic triangle with two men, Diane’s Republican husband (played by Gary Cole) and a doctor (played by John Slattery) who gives her microdoses of a hallucinogen to help her deal with the stress of voting rights being threatened and Roe being overturned).

Ms. Baranski said she gushed to Ms. King: “My God, I’ve just had the most wonderful day at work. I was in bed between Gary Cole and John Slattery.”

In one scene in Season 4, Diane got dolled up in a black vinyl dominatrix catsuit for her husband, Kurt, a taciturn conservative who works for the Trump administration and the N.R.A., and who goes big-game hunting with the Trump sons and gets shot, Dick Cheney-style.

“Thank God for Pilates and talcum powder,” Ms. Baranski said dryly. “It took four dressers and a lot of talc to get me in and out. This outfit deserves more than one orgasm.”

Though Kurt’s political ideology causes Diane agita, she is determined to reach across the chasm. When he is dubious about the dominatrix outfit, she switches to “an N.R.A. Barbie” look, adding a cowboy hat and a rifle.

“It’s a way of keeping things lively in the bedroom,” Ms. Baranski explains, “since they dare not talk politics in the dining room.”

Mo Rocca, who has guest starred on “The Good Fight,” told me: “You don’t think, ‘This is sexy for an older couple.’ You just think it’s sexy. She’s getting better as she gets older, which I think is really cool.”

In an era when many college students polled say they would refuse to share a dorm or go on a date with a student from the opposite party, Diane and Kurt seem to be the only red-blue blend in America that’s working.

Diane consults with the ghost of Justice Ruth Bader Ginsburg, complete with the white lace collar on her black robe — played by the wonderful Elaine May — to get advice on how she managed to maintain a friendship with Justice Antonin Scalia.

The Ginsburg ghost tells Diane that Justice Scalia teased her and made her laugh and cooked “amazing” pasta, adding, “Life is too short to fight over everything.”

In one particularly inventive episode, the Kings conjured an “It’s a Wonderful Life”-style world, where Diane is knocked out and thinks her idol, Ms. Clinton, has won the election. Diane is shocked to learn her firm is representing Harvey Weinstein because there has been no #MeToo movement; the women he attacked were too afraid to come forward, given that President Hillary Clinton has given the predator and donor the Presidential Medal of Freedom. But, on the positive side, the polar bear population is expanding.

“One of the great things about that character,” Ms. Baranski said of Diane, “is that she was never portrayed as a victim. I don’t like playing victims. I’d be terrible as the long-suffering wife.” She said that’s also why she liked playing Maryann Thorpe, who “had her three-martini lunches and then planned creative revenge on her ex-husband.”

I ask Ms. Baranski about her Tiffany’s window of laughs. She has about 12 different ones, all sparkling — ranging from sultry to sarcastic to can-you-believe-Donald-Trump-might-run-again?

“I like to be known for my laugh,” Ms. Baranski said. “My laugh and my legs, that would be my legacy. Laugh, legs, legacy. I always said if I could be photographed from the waist down, I’d have a great film career.”

Confirm or Deny

Maureen Dowd: You were named Miss Kielbasa in 1970.

Christine Baranski: No, but I did get the Polish Ham Award and was sent a ham.

You gave Elon Musk the hairy eyeball at the Met Gala.

My daughters gave me a photo of it as a Mother’s Day present. I don’t know him. It just makes me angry that billionaires spend all their money trying to get to space when there’s so much work to do down here.

Losing to Maggie Smith at the 2012 Emmys was one of your major career achievements.

The idea of Maggie Smith as a supporting actress really is laughable. She’s my idol. I saw Laurence Olivier’s “Othello” in downtown Buffalo and this actress named Maggie Smith was playing Desdemona. I followed her career. I think she’s just the consummate technician.

You were excited to do a scene with your crush Colin Firth in “Mamma Mia!”

I was in a red Norma Kamali bathing suit floating in a little water dinghy. We were out at sea, and so I had him all to myself. And it was one of those wonderful moments where you think, “I can’t believe I’m doing this.” I love Englishmen. I think I was British in a former life.

When you worked with Cher in “Mamma Mia! Here We Go Again,” she called you “a high-kicking bitch.”

Yes, how great is that?

When Tom Stoppard did the play “Hapgood,” you tried for a part.

The play is about quantum physics. I wrote him a note: “Dear Tom, I hear you’ve written a play about quantum physics. Is there a particle for me?”

You’d stand in zero-degree weather if it meant you got to watch the Buffalo Bills beat the New England Patriots.

Absolutely.