Wash the grapes, drain well and pluck them from the stalks. Cream fat, 200 g sugar, salt and vanilla sugar with the whisk of the hand mixer. Stir in 4 eggs one after the other. Mix flour and baking powder and stir in alternately with the milk.
Spread into a greased, floured fat pan of the oven (36 x 42 cm; 3 cm deep). Spread 500 g blue grapes on top.
Stir sour cream, 6 eggs, cream, white wine, pudding powder and 100 g sugar until smooth. Spread the sour cream mixture over the grapes and bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 45 minutes.
Remove and let it cool down.
Cut the cake into pieces and decorate with the remaining grapes. Dust with cocoa powder.