Melt 120 g butter. Mix flour, 125 g sugar, baking powder and cocoa powder. Add egg yolk, 4 tablespoons lemon juice and melted butter. Use the dough hooks of the hand mixer to make crumbles, chill. For the filling, drain the mandarin oranges.
Separate the eggs. Mix 60 g butter and 75 g sugar until creamy. Add 6 tablespoons lemon juice, egg yolks, semolina and quark and mix. Beat the egg whites until stiff. Fold the beaten egg whites and fruit into the quark mixture. Put 3/4 of the crumbles into a square springform pan (23 X 23 cm), press it down a little. Fill in the quark mixture. Sprinkle the remaining crumbles on top. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 1 hour, then let cool down.
Put 3/4 of the crumbles into a square springform pan (23 X 23 cm), press it down a little. Fill in the quark mixture. Sprinkle the remaining crumbles on top. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 1 hour, then let cool down. Dust mint with cocoa. Decorate the cake with it