To make chocolate curls, which star in this Black Forest Cake, my Bûche de Noël (Yule Log Cake), and also make for a stellar sundae topping, use a vegetable peeler to shave the edge of the chocolate bar for narrow curls. Or flip the bar to shave the side wide curls. Curls can be refrigerated or kept at room temperature for a short amount of time before layering on this cake.