Of course not. If you have a favorite white cake recipe, by all means use that one. You can even use a box mix if you'd like. And if you prefer a different peanut butter buttercream recipe, go for it. You can even make the mallow with a different recipe and/or switch up the flavors if you want. Make a peanut butter and jelly cake by adding some raspberry or strawberry puree or freeze dried fruit whizzed to dust in a blender to your mallow, for example.