Ice cake. Using confectioners’ sugar, stiffen 4 cups icing to medium consistency. Ice cake smooth. Using notch side of comb, comb cake.
Using black icing color, tint 1 cup chocolate icing black. Prepare decorating bag with black icing. Cut ½ in. off tip of bag. Pipe icing into indents of cake. Using icing smoother, smooth out icing, wiping smoother clean after each use.
Let icing crust, at least 1 hour.