Cut one cake layer in half as shown in Diagram 1 of Sombrero Cake
; cut remaining cake layer as shown in Diagram 2. Arrange both Brim pieces, the Top piece and Base of Brim piece on cake board or large platter as shown in Diagram 3 to resemble sombrero. Cut Band and Mustache pieces horizontally in half to make two pieces of each. Place both Band pieces on cake as shown. Reserve both Moustache pieces for later use. Spread 1-1/4 cups of the frosting evenly onto all cake pieces except mustache. Refrigerate or freeze until frosting is firm. Meanwhile, melt chocolate as directed on package.