Beat the egg whites with granulated and vanilla sugar to a stiff foam, gradually beat in one yolk after another and beat thoroughly after each one. Add oil and water and finally mix in flour mixed with baking powder. Separate half of the dough and add cocoa to one part.
Pour the white part of dough onto a greased and floured baking sheet (approx. 10 x 13 inches) and layer the cooked chocolate pudding on top. Make piles and layer the cocoa part of dough.
Bake in a preheated oven at 355 °F / 180 °C until the edges start to come away from the sides of the baking sheet.
Layer the sour cream mixed with granulated and vanilla sugar on the still hot baked cake. Smooth it well and let it cool, preferably let it rest overnight in the refrigerator.