Chop 100 g chocolate and melt over a warm water bath. Cream fat, 200 g sugar and vanilla sugar with the whisk of the hand mixer. Stir in 4 eggs one after the other. Stir in the chocolate.
Mix flour and baking powder and stir in alternately with the milk. Smooth in a greased, floured fat pan of the oven (36 x 41 cm).
Drain the mandarins, drain well. Wash lemon, grate dry and grate peel. Halve lemon and squeeze juice. Separate 5 eggs, cover the egg whites and chill. Mix quark, lemon peel and juice, 100 g sugar, 5 egg yolks, 1 egg and pudding powder.
Halve the quark mixture. Stir the mandarins into one half and spread carefully on the dough. Spread the rest of the quark mixture on top. Bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see
manufacturer) bake for about 30 minutes.
Chop 75 g of chocolate and melt over a warm water bath. Beat the egg whites with a pinch of salt until stiff, adding 150 g of sugar. Take the cake out of the oven and spread the beaten egg whites on top.
Spread chocolate on top and swirl with a fork. Bake at the same temperature for a further 10 minutes, remove from oven and let cool on a cake rack.