Claire Ptak first learned about Meghan Markle through Ms. Markle’s former lifestyle blog, The Tig, a so-called hub for the discerning palette that she started in 2014.

After Ms. Ptak, the owner of Violet, a cafe and bakery in London, published “The Violet Bakery Cookbook” in 2015, she sent a copy to Ms. Markle, who later asked to interview her.

“Great questions,” Ms. Ptak, 48, said of that conversation.

Ms. Ptak had by then been living in London for about a decade. Raised in Northern California, she moved to England soon after she married a Briton in 2005, and opened her bakery in 2010. (She is now divorced.)

In 2018, Ms. Ptak was asked to make what has probably become her most famous dessert: a lemon and elderflower cake served at Meghan and Prince Harry’s wedding. Last year, Ms. Ptak made a version of the cake for a birthday party for the couple’s daughter, Princess Lilibet Diana.

“Claire’s desserts are more than just a conclusion to a great meal; they’re bites of special memories for me,” Meghan, the Duchess of Sussex, said in an email. “Her cakes have been at the center of some of our most cherished family moments.”

The recipe for the wedding cake is featured in Ms. Ptak’s new cookbook, “Love Is a Pink Cake.” (The cookbook, Ms. Ptak’s fifth, shares a title with a series of drawings by Andy Warhol.)

While home bakers may now have the recipe for the dessert, few if any will be able to prepare it exactly as Ms. Ptak did for Harry and Meghan. Ms. Ptak baked it at Buckingham Palace, with ingredients including an elderflower cordial made at Sandringham, the royal family’s private estate in Norfolk, England.

The cordial, Ms. Ptak said, tasted “better than any other elderflower I’ve ever had.”

Though Ms. Ptak’s royal wedding cake may be her most talked-about dessert, another she made more recently, for the makeup artist Isamaya Ffrench’s birthday, also generated some buzz. The cake was shaped like a penis, covered in silver fondant and decorated with sterling silver leaf.

“We made it in the window of the bakery, and it really made people crack up,” Ms. Ptak said.

Like the cake she made for Ms. Ffrench, “Love Is a Pink Cake” offers glimpses of Ms. Ptak’s personality, as well as of her personal life.

The cookbook’s sections, California and England, are based on the two places she has called home. For some of its recipes, she took inspiration from dishes made by peers in the food world, like a chocolate hazelnut cake inspired by her favorite dessert at the River Café in London, where Ms. Ptak answered phones when she moved to the city.

Other recipes in the book came from moments in her life: mornings hung over in Paris, a granola mishap at Violet and advice Ms. Ptak received from the actress Frances McDormand — to “stick to tequila” instead of drinking wine — which in part inspired Ms. Ptak’s recipe for a tequila pumpkin pie.

Ms. Ptak worked with two photographers, Maren Caruso and Pia Riverola, to produce the cookbook, which features images that are rich in color (a pistachio-green plum cake with candied violets) and texture (a “furry” coconut frosting, as Ms. Ptak put it).

Ms. Ptak likes to use in-season ingredients in her baking, and she is in regular contact with the farmers who supply the fruit. It’s an approach that stretches back to her childhood, when she would forage for wild blackberries and huckleberries and use them to make pies with her mother.

Decades later, she refined her baking philosophy as a pastry chef at Chez Panisse, a restaurant in Berkeley, Calif., recognized as a pioneer in the farm-to-table movement.

Alice Waters, the founder of Chez Panisse, described Ms. Ptak as someone who obsesses over fruits as they come into season. Ms. Waters said that Ms. Ptak will compare the taste of apricots grown on different farms, for instance, or how the sweetness of berries changes from one week to the next. “It is this sort of curiosity that makes her such a thoughtful cook,” Ms. Waters said.

Before Ms. Ptak opened her bakery in London, she sold baked goods from street stalls at the city’s Broadway Market. In the years after she opened Violet in Hackney, a borough in the East End, the neighborhood became one of London’s trendiest areas.

The fashion designer Simone Rocha, who used to live down the street from Violet, said she was a fan of the bakery for years before meeting Ms. Ptak. Ms. Rocha often uses Ms. Ptak’s recipes for prune scones, banana bread and Victoria sponge cake.

Christopher Kane, a fashion designer who lives and works near Violet, is another fan. This year, he and Ms. Ptak designed a purple tote bag sold at the bakery; it says, “more cake.” There are plans for a pink version in honor of the new cookbook.

Ms. Ptak said that after arriving in London she was surprised to learn that people there loved cake so much. “I think it’s why I like it here,” she said.