The panini arranged in soft mounds in the vitrine of Sant Ambroeus on Madison Avenue fairly ooze. There is the tuna, decadently layered with marinated artichoke; the pillowy frittata; the turkey stacked high with mozzarella and tomato and shellaced with Dijon mustard, all as savory looking as they are seductive.

As they should be, said Gherardo Guarducci, a partner in the SA Hospitality Group who, with Dimitri Pauli, owns the Sant Ambroeus restaurants seeded throughout Manhattan and in prosperous enclaves throughout the country.

“Food has given me some of the greatest moments of pleasure and prayer in my life,” said Mr. Guarducci, who is the more public face of the company. “It can provide a feeling of nurturing, silence, spirituality and a satisfaction that is much like sex. I can never have enough.”

You could say he overcompensates. He and Mr. Pauli have embarked on an expansion of late, their empire now stretching to encompass new Sant Ambroeus outposts in East Hampton, N.Y., which opened in November, and Aspen, Colo., which will open this week. Among other recent projects is a two-story Sant Ambroeus in Brookfield Place that opened in November 2020. It is a quick stroll from the World Trade Center, home to Condé Nast.

The partners are considering a location on the Upper West Side of Manhattan. There is also the more casual Felice, with 11 locations in New York and Florida.

But the jewel in the partners’ crown is the newly restored Casa Lever, the former Lever House restaurant, owned and managed since 2009 by the SA Group, and situated on the ground floor of the totemic Lever House on Park Avenue. Their most lavishly upscale venture to date, the restaurant, which reopened last week after a monthslong hiatus, has been spruced up with a $3 million investment, the financing shared among SA Hospitality Group, Brookfield Properties and the WatermanClark investment group.

Like Sant Ambroeus, it has long been a magnet to personalties at the top of their professions, not least those in the notoriously capricious world of style. Now, as at its debut, one enters by way of a tunneled ramp that opens on a long dining room warmed with wood-slatted walls, black leather banquettes and discreet accents of pumpkin. Alcoves along one wall promise a touch of seclusion.

The setting is paradoxically cozy and theatrical, faithful to the original Marc Newson design but minus the feverishly colorful Andy Warhol portraits that once animated the room. (Silk-screened works, they belong to the real estate magnate Aby Rosen, who sold Lever House in 2020.) In their place will be a selection of Damien Hirst butterfly canvases and other blue-chip works. Imposing Ellsworth Kelly sculptures shield the garden from interlopers’ eyes.

Setting is critical, for Mr. Guarducci subscribes to the popular wisdom that fine dining is like show business, an attraction for gawkers of varying stripe. At Casa Lever, as at Sant Ambroeus, “people-watching is very important,” he said. “You come to be in the company of the titans of finance, real estate or the art world, because these people are powerful or famous — or because they are your kind.” Either way, the experience confers “a sense of belonging,” he said.

As scenes go, Sant Ambroeus initially provided the template. “It’s very clubby in a slightly snobby European way,” said Ed Burstell, a retail and beauty branding consultant. The crowd, dense at breakfast time, picks up steam later in the day, Mr. Burstell noted. “There will always be a ‘somebody,’” he said. “It’s a guaranteed sighting.”

Diners at the restaurants, who at various times have included Tom Ford, Carine Roitfeld, Thom Browne and Grace Coddington, provide a veneer of glamour and dynamism. “Fashion people set a lot of ideas — I don’t want to say trends — for the community,” Mr. Guarducci said. “You experience the restaurant differently when the fashion world endorses it. You approach it with a more open mind.”

Fashion, however, can also lend an unwelcome air of elitism, as was observed in a 2010 New York Times two-star review of Casa Lever. A restaurant of the Manhattan old school, Casa Lever, the critic noted, “is built for socialites and those who finance them, staffed by handsome, rakish men with huge wristwatches.”

Mr. Guarducci brushed off that long-ago slight like a dusting of lint. “It was what you would expect,” he said. “It highlighted the fact that we are not for everyone.”

Spoken like a haughty impresario. With his patrician features, springy salt-and-pepper hair and lean 6-foot-4-inch frame, Mr. Guarducci, 56, looks the part. But he seems at pains to counter that image.

“I did spend some time thinking about how formal I should be for this interview,” he said. “These are the clothes that I normally wear,” he said of his deep blue Zegna blazer, Aspesi corded trousers and brown suede Tom Ford shoes.

That muted look, he suggested, is well in line with his Tuscan-bred reserve. “I’m not a particularly social being,” he said. And while his career has afforded him entree into society’s upper echelons — “I’ve met and had moments with everybody, from Bloomberg to the president,” he said — he describes himself, work aside, as something of a recluse.

To ease the built-in pressures of the work, he spends swaths of time at home with his wife, Samantha Tannehill, a model turned interior designer. There are visits as well from his four children from an earlier marriage, who range in age from 22 to 30. He seeks balance most mornings through a form of Vedic meditation. “And then I pray,” he said.

The son of a textile entrepreneur, Mr. Guarducci expected to enter the family trade in the manufacturing town of Prato, but when that business faltered during the early 1990s, he decamped for New York. He has rarely looked back.

For a time he sold focaccia sandwiches in Bryant Park, where the fashion week shows were held. “I came to depend on Fern Mallis,” he said of the executive director of the Council of Fashion Designers of America at that time. “She would decide when they set up the fashion week tents, whether my kiosk would become part of the show. I stayed and served focaccia to the fashion crowd.”

In the early 2000s, he approached the Pauli family, then the owners of Sant Ambroeus, with the idea of reopening Sant Ambroeus on Madison (the canvas-tented original had closed in 2003). He and Mr. Pauli went on to found a series of sister restaurants in the city.

The venture thrived despite setbacks. “Covid arrived at the height of our success,” Mr. Guarducci said. “The time was physically, mentally and emotionally so trying that it actually aged me.”

He persists, though challenges remain. “We are the only business that needs to be excellent at managing all your senses — what you see, smell, hear and taste,” Mr. Guarducci said. “If the bread is stale or the room is loud, if any one of those things is off, you’re going to feel that the food isn’t that great.”

Dining, he knows, tends to be an immersive experience. “As in any form of theater,” he said, “you are only as good as your last performance.”