Fed up with fusion, chefs have gone back to the cutting board to lift the all-American hamburger from basic to big-time. New York Burger Co. in Manhattan does a fast-food version, subbing in upscale toppings aboard its naturally raised, hormone-free beef patty (212-254-2727). New to Chicago, Masck grills a thin, playfully oversize, bun-bursting “floppy burger” (312-440-8880). And at Father’s Office in Santa Monica, the resident beer sommelier will perfectly pair a Belgian ale with the house dry-aged-beef burger sporting caramelized onions, Maytag blue cheese, and arugula (310-393-2337). Slumming it never tasted so good.