Melt the butter and let it cool down briefly. Beat eggs in a bowl. Add the milk, sugar and salt and whisk in quickly with the whisk, mix in the butter. Sift the flour, cocoa, starch and baking powder over it and stir everything into a smooth batter.
Chop the chocolate, chop the banana and fold into the batter.
Let the dough soak for about 10 minutes. Bake in portions according to the instructions for the waffle iron.
Dust with powdered sugar and serve with cream, ice cream or fruit compote as you like.