The cupcake is America's darling. It's celebrated in upscale bakeries, on Sex in the City , on the cover of Gourmet , and in thou-sands of classrooms--where every day, it seems, a parent has sent in a batch for the kids to share. The very word conjures up whimsy, coziness, pleasure, nostalgia. Not to mention the fact that their diminutive size means you can eat a lot of them. Once upon a time, a family had only two recipes for cupcakes--chocolate...