Pour in the milk and butter. Beat the mass again. Gradually introduce flour mixed with cocoa and baking powder. The finished dough will turn out to be quite liquid, but you do not need to add more flour, otherwise the biscuit will not turn out delicious.
Pour the finished dough into a baking dish and bake in the oven at 180 degrees for about 30-40 minutes. check the readiness with a dry wooden skewer.
Let the hot biscuit cool, take it out and shape it. Wrap in plastic wrap and refrigerate for at least 12 hours. Cut the sponge cake into 3 cakes.