Preheat the oven according to the package instructions.
In a large bowl, add the ingredients according to package instructions. Grease the pan or oven-proof glass baking dish with butter.
Add the cake batter to the pan and bake in a preheated oven according to the package instructions. Let the cake cool (while still in the pan).
Cut about 1/3 of the cake into cubes (1-inch square) and set aside. There will be extra cake left over.
After the cake has cooled and you're ready to assemble the desserts, make the frosting and then the ganache.