You will never again look at the classic peanut butter-and-jelly brown-bag sandwich without thinking of this witty (and mouthwatering) semifreddo cake. This confection features white butter cake (the "sandwich bread"), airy peanut butter mousse, and blueberry mousse made with pureed fresh fruit. Strained jam is spread on top as a glaze. Store the confection in the freezer, then display it a half hour before cutting so it can warm up, suggests contributing editor and pastry chef Jason Schreiber. Then serve this version of PB&Js in 1-by-2-inch slices. "You don't need a big piece," Schreiber adds. "It's a very rich cake."