Mix the eggs, sugar, vanilla sugar, milk, butter and cocoa powder well. Sieve the flour and baking powder and fold in a spoonful.
Spread the mixture on a baking sheet and bake at 200 degrees for 20 minutes.
During the baking time, stir together powdered sugar, coffee, cocoa powder, vanilla sugar and butter to a smooth mass. Spread this mixture on the still warm sheet cake with a brush. Scatter coconut flakes on top.
After the cake has cooled down, cut it into pieces.