In the meantime peel, halve and core the apples and cut them into pieces. For the sponge mixture, whip the fat, 250 g sugar, salt and vanillin sugar until creamy with the whisks of the hand mixer.
Stir in 4 eggs one after the other. Mix flour, starch, baking powder and cocoa powder and stir in portions with milk. Spread the dough evenly on a greased fat pan of the oven (32 x 39 cm).
Sprinkle with apple pieces. Spread cranberries in splotches on top. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 15 minutes. For the icing, mix 2 eggs, sour cream, sauce powder and 50 g sugar.
Pour the icing on the pre-baked cake and bake for another 15-20 minutes. Remove and let cool on a cake rack.