Daniel Boulud's "casual bistro" (it's neither, really) consists of two elegantly appointed rooms, one in front where the tables are not clothed, and one in back where they are. The menu is organized by the French names of seasonal ingredients -- lobster (homard), beet (betterave), beef (boeuf), and mushroom (champignon), par exemple. Within each category, appetizers and main courses are listed. Much has been made of the $29 hamburger. But considering it is superbly stuffed with braised short ribs, foie gras, and black truffles, it's almost a deal. Reservations essential. Subway: B, D, F, V to 42nd Sts.