Use a 2-layer cake mix to bake 2 (8- or 9-inch) round cake layers. Cool completely. Use 1 of the cake layers as directed. Wrap remaining cake layer tightly in plastic wrap, then in foil. Store in freezer up to 1 month.
How to Slice Cake Layer Evenly
Place cooled cake layer on serving plate. Make a 2-inch horizontal cut around side of cake using a long serrated knife. Then, cut all of the way through the cake layer to make 2 layers.