If the goal is to avoid eating an entire baguette in one sitting, stay away from Chelsea Green. In this quaint micro-neighborhood of southwest London known for its specialty-foods shops, hospitality impresario Robin Birley (of 5 Hertford Street and Oswald’s fame) and his longtime executive pastry chef, Vincent Zanardi, have opened Birley Bakery.

Whether contending with the seven a.m. rush or the after-school-snack crowd, the place is never dull. (And that is not only due to its dazzling array of seeded baguettes, hand-dipped chocolates, and Paris-Brest.) Since its January 6 opening, this boulangerie-pâtisserie on Cale Street has established itself as an epicenter of a rarefied universe. Even those highly maintained Chelsea types who swear by the ketogenic diet (in theory) are lining up for cinnamon croissants glazed with caramelized sugar. Jesus, take the wheel …

Robin Birley, photographed by Jonathan Becker, and his executive pastry chef, Vincent Zanardi.

Birley Bakery’s warm and welcoming design invites everyone to hang around. At first glance, it feels like a familiar French establishment, but, in true Birley fashion, the interiors are more layered than that. The artist Lizzi Porter hand-painted murals on the crimson walls, and the light fixtures and displays nod to 19th-century Oriental design. Every element of the experience has been considered in great detail; even the striped take-out boxes designed for Zanardi’s orange-blossom-scented tartes tropéziennes feel like the stuff of a Wes Anderson film.

Birley Bakery’s popularity is no accident; the idea was born from the flour-based fervor that led members of Birley’s private clubs in Mayfair to consume an average of 550 bread rolls per day. For the past 12 years, Zanardi’s indulgences have proved so irresistible that even a well-mannered titan of industry has been known to stash after-dinner chocolate shards in her Fendi clutch. (Not like anyone would ever gossip about it.)

Come for the carbs. Stay for the ambience.

Now Zanardi and Birley are delivering the goods to the masses as well as the members. “It’s very exciting, but very stressful,” says Zanardi, declining an offer to split a little something fresh from the oven. “In a private members’ club, you work for just a few thousand people, not the whole public. Now, I’m finally showing what I’m doing, and I had no idea if they were going to like it or not. It’s also nice to finally meet the people I’ve been cooking for for the past 11 years.”

Even a well-mannered titan of industry has been known to stash after-dinner chocolate shards in her Fendi clutch.

Zanardi has been preparing for this moment. Raised in a small village outside of Paris, he grew up relishing a warm baguette eaten on the walk home from school. His mother’s fraisier, a traditional French cake made of kirsch-soaked sponge, crème pâtissière, and fresh strawberries, led to an infatuation with pastry. After training for two years in a restaurant kitchen, he moved over to the pâtisserie world and eventually to the universe of Joël Robuchon, who relocated him to London in 2006.

A stylish place to break bread.

Today, Zanardi spends much of his time behind the counter in Chelsea Green, but he also oversees a 15-person team at the industrial bakery in nearby Pensbury that feeds all of Birley’s projects. On a recent Wednesday morning, in anticipation of Valentine’s Day, a chocolatier was spray-painting nut-and-caramel filled hearts with a fine dusting of red pigment. “We’re sneezing chocolate,” said executive pastry chef Francesco Coratella with a smile, inhaling the scent. Nearby, a congenial crew folded croissant dough and cranked out 5 Hertford Street’s signature churros from a steel press.

The Birley Bakery operation has been years in the making; there is now discussion of opening a branch in New York City alongside Maxime’s, the Upper East Side dining club that will open at some point this year. “As you can imagine, Mr. Birley is very specific and picky; that’s probably why he’s so successful,” says Zanardi. Birley, who loves a good pork-hot-dog cravat, concurs: “It’s an obsession we share in everything we do.” That’s why the pistachio spread is sourced from Sicily, the wheat flour from Burgundy, the almonds from Valencia, and the sea salt from La Guérande, in Brittany.

Some of Zanardi’s signature creations, including the much-discussed Paris-Brest (fourth row from top).

The results are so good you can taste them. Zanardi, in fact, spends much of the day doing so—but only small bites, he swears. As for how he stays so trim, despite the endless opportunities to self-sabotage? “It’s the shape of the jacket,” he said, straightening out his lapels. “It’s from a very good brand. But also, I’m a savory person.”

Ashley Baker is a Deputy Editor for Air Mail and a co-host of the Morning Meeting podcast