For the banana cake, preheat the oven to 180 °C top/bottom heat. Cream butter with powdered sugar, gradually add eggs and continue beating until creamy.
Mash the bananas with a fork and stir them in. Mix milk with baking cocoa, mix flour with baking powder. Stir these ingredients into the banana mixture.
Pour the batter into a greased and floured pan and bake for about 45 minutes. Cover the cooled banana cake with chocolate icing.