Mix the sugar, vanilla sugar, eggs and margarine with the mixer until frothy. Then add flour, baking powder and sour cream or natural yoghurt.
Pour half of the dough into a loaf pan that has been greased and sprinkled with breadcrumbs. Mix the second half of the dough with the cocoa powder and also fill the loaf pan.
Bake the cake in a preheated oven at 180 ° C - 200 ° C for approx. 60-70 minutes.
After a baking time of approx. 10 minutes, cut into the cake lengthways approx. 1 cm with the tip of a knife.