One bite of a kouign-amann from Alexander's Patisserie will dispel any doubts you may have about the quality of a French patisserie run by a restaurant group best known for its high-end steakhouses.

It's flaky, buttery and sugary in all the right ways. Kouign-amann is the croissant's younger, prettier sister — made from the same layered dough, but dusted with sugar and salt and baked in muffin tins. The result is a caramelized, crunchy top and buttery soft center (the literal translation of kouign-amann is "butter cake") — a balance, I hear, that is difficult to achieve.

But they've done it at the nascent Alexander's Patisserie in downtown Mountain View, which opened in mid-October and promptly sold out of kouign-amann, croissants, macarons, tarts and cakes for several days. This was partially due to hype, and partially due to the staff not being able to get into the kitchen to prep as early as they had hoped. Almost one month after opening, they're still trying to catch up with the demand. (Alexander's Director of Public Relations Marilyn Skinner said last week they're now only selling out on weekends.)

The Castro Street patisserie is the first venture of its kind for the Alexander's Steakhouse group, which operates restaurants — all steakhouses save for one — in Palo Alto, San Francisco and Cupertino, with two more on their way in Pasadena and Shanghai.

The man behind the Alexander's pastry case is Dries Delanghe, a 26-year-old soft-spoken pastry chef from Belgium who has known he wanted to bake for a living since he was 12. Delanghe's career spans continents and industries, from a hotel in Brussels to a stint with macaron king Pierre Herme in Paris, and most recently, four years at three-Michelin-starred Joel Robuchon Restaurant in Las Vegas.

"Always as a kid when I would go to a bakery and buy bread, I would want to slice it myself," Delanghe said. "I was always interested in how they make it — like, how do they get the filling inside of a cake?"

So, at the ripe age of 12, he told his parents he wanted to go to pastry school. They turned him down, telling him he would be sick of it by the time he was 18. Two years later, he had the choice of attending again, and he off he went.

Delanghe has big plans for Alexander's Patisserie. The full, impressive menu lists 14 flavors of macarons, four kinds of brioche, waffles, madeleines, quiches, sandwiches, salads, tarts, focaccia and loaves of fresh bread, both sweet and savory. Delanghe wants to bring suikerbrood ("sugar bread" in Dutch) to Mountain View: a traditional bread from Holland that Delanghe describes as "kind of like a brioche," but with sugar mixed into the dough.

"When it bakes, it has pockets of sugar and butter mixed into it," he said. Sign me up.

Delanghe's ultimate vision for Alexander's is that it be a one-stop shop for fresh bread, classic French pastries, chocolates and macarons. Everything is made in-house and on-site.

"I like to say it's four shops in one," he said.

Stroll into Alexander's currently and you'll likely find macarons ($2 for one, $13 for six, $25 for 12), chocolate and regular croissants, kouign-amanns, canele, perhaps two types of small desserts called entremets, brioche loafs and a few exquisite tarts and cakes (mostly $6). The patisserie partnered with San Rafael-based Equator Coffees & Teas to create their own line of blends; there's also hot chocolate and loose leaf tea.

At the shop in late October, a row of large glass pastry cases remained awkwardly empty. Delanghe said his staff had doubled production, but were still struggling to keep up with the demand.

Delanghe sees the spacious patisserie, decorated in a white-and-black theme with marble-topped tables, elegant white chairs and chandeliers, as a cross between a classic French patisserie and a modern American coffee shop. He hopes customers will come in to enjoy a leisurely pastry and coffee, while others will get their desserts to go or come in after eating dinner at one of Castro Street's many restaurants (Alexander's is open until 10 p.m. Thursday through Sunday).

"We wanted something different that hasn't been seen here before in Silicon Valley," Delanghe said. "There are a lot of bakeries and some pastry shops, but not the whole concept where you can find everything from bread to chocolates and dine in or to-go and sit in a nice environment."

This reporter, for one, is very excited for when Alexander's does indeed reach the point of being "the whole concept."

Alexander's Patisserie

209 Castro St., Mountain View

650-864-9999

alexanderspatisserie.com

Hours: Sunday-Wednesday, 6 a.m. to 8 p.m.; Thursday-Saturday, 6 a.m. to 10 p.m.