This classic Creole bistro, run by members of the Brennan family, was one of the last old-line restaurants to reopen after the storm. Other places make fine chicken and andouille sausage gumbo or barbecue shrimp, a local specialty of jumbo shrimp sautéed in a pool of butter. No one, though, does those dishes as well as Mr. B’s. Now that it’s back, both the socialites and downtown businesspeople have returned to this favored destination for long, cocktail-fuelled Friday lunches that last all afternoon.