Prepare a round spring form (22-24 cm) with butter and bread crumbs.

Mix water, butter and cacao in a saucepan. Heat until butter is melted and let cool down.

Whisk sugar and egg in a bowl.
Mix flour, baking powder and salt in a separate bowl.
Add the flour mixture and chocolate mixture to the egg and milk, mix to a smooth batter.

Bake for 25-35 minutes. Use a cake tester to see that it comes out clean, then you know the cake is ready.

Let the cake rest 10 minutes before removing it from the spring form and let cool completely. 

Decorate with icing sugar and cacao (optional).