My daughter asked for a butterfly cake for her birthday this year. It is easier than it might look, you can basically make it with any type of round sponge. If you have 2 springform tins of the same size, you can bake them at the same time, otherwise, bake them in the same tin, one after the other. It is best to bake the sponge the day before and wrap it in cling wrap, it is easier to fill when it is not freshly baked.