Two days earlier, the restaurant’s unassuming facade was still covered with building permits. Inside, a long, narrow, warmly lit room was lined on one side by white oak booths and on the other by a long bar meant for wine and charcuterie (prepared meats, mostly pork, which Mr. Boulud’s longtime publicist Georgette Farkas called “a separate-the-men-from-the-boys-kind-of-food”). The vaulted ceiling gave the place the feel of a very expensive, chic railcar. Servers hunched quietly in the back of the room around Daniel Johnnes, Mr. Boulud’s wine director.

Downstairs in the basement kitchen, no fewer than 30 pastry chefs and sous-chefs were attending to the raw meat covering the counters and the vegetables cooking in a massive tilt braiser, and the smell of coq au vin permeated the room. Mr. Boulud, perhaps Manhattan’s best-known ambassador of haute French cuisine, emphasized there were limits on his interpretation of casual. “Many of us—Eric [Ripert, of Le Bernardin], Jean-Georges [Vongerichten], we were raised in the three-star [Michelin] model,” he said. “And of course we know how to have fun. But I’m never going to be the kind of guy who’s going to slap your food on the table … where the kitchen is small and dirty and the ingredients are so-so. A designer who has a big brand name, even if he goes into the casual thing, he can’t make clothes with cheap fabric. The fabric is very important.”

Or, as Ms. Farkas put it: “The great haute couture designers don’t do ready-to-wear until they’ve established their reputations.”

On New Year’s Eve, Mr. Boulud was planning to visit all four of his Manhattan restaurants, in a trajectory from east to west. “I start at Daniel, then I go to Café Boulud, then Bar Boulud and DB [Bistro Moderne],” he said. Then he would return to Daniel—“for the big bang.” Among his clique, he we was alone in this show of commitment. “Jean-Georges is in St. Barth’s. Maybe next year I’ll take the same route. Eric is never open for New Year’s because of Times Square. He just called from the beach.”

After the New Year’s sneak preview, Mr. Boulud planned to roll out his version of “ready-to-wear” on Thursday, Jan. 3, to a select group of fellow chefs (Mr. Ripert, Mr. Vongerichten and Per Se’s Thomas Keller are all invited) and to his best customers, as well as a few opera and ballet performers from Lincoln Center, who he hopes will find a late-night gathering place in Bar Boulud. In February, he’s off to Beijing, where he plans to open Maison Boulud in the spring. At the end of the summer, he’ll unveil a burger spot in the Bowery, down the street from the site of the now-defunct nightclub CBGB. It may or may not be called DBGB.