A few years ago, my mom—an elementary-school lunch lady—bought me one of the heavy-duty aluminum cookie trays she uses at work. Made by a company called Central Restaurant Products, it retails for $34.19. Because this is a ludicrous price for a cookie sheet, I got only one. Thus, half of every batch of cookies I make goes onto a flimsy sheet from Wal-Mart. And every time, the cookies baked on the Cadillac of cookie sheets come out perfectly, while the cookies baked on ol’ cheapo emerge with woefully burned edges. To find out why, I bribed a few Northwestern engineering grads with cookies. They say it has to do with the thickness of the pans. On a thin pan, the uncovered metal surface heats up more quickly than each thick ball of cookie dough, singeing the edges of each cookie before the middle is done. On a thicker pan, the uncovered surface heats up at a similar rate to the dough, making for a more even bake between center and middle. Looks as if good dessert really is a perfect science.