Mix the flour, butter, sugar, cocoa powder, egg and baking powder well in a mixing bowl. Spread 2/3 of the dough in a greased and floured cake tin, press down lightly and form a small edge on the side.
For the filling, mix the butter, sugar, quark, eggs, vanilla sugar and custard powder to a smooth mixture. Spread the filling on the bottom. Crumble the remaining dough onto the filling as a crumble.
The cake is baked at 175 ° C (convection) for about 1 hour.