Mix soft butter with icing sugar, add the yolks one by one and stir everything until creamy.
Stir in the flour and starch, cocoa, rum and milk mixed with baking powder - spread the dough into a prepared 20 tin.
Heat the oven to 160 ° convection.
Prepare topping:
Beat the egg white into firm snow, add the sugar and whip in vigorously, gently stir in the coconut flakes.
Spread the coconut topping on the dough, bake in a preheated oven at 160 ° for about 30 minutes (stick test) - thinly spread the warm cake with the warmed jam and sprinkle with coconut flakes after about 15 minutes.