Mix the eggs, sugar and cocoa powder, melt the margarine and add. Then add sour cream, flour and baking powder. Mix everything into a dough and divide between 2 baking trays. Bake at 180 degrees for 15 minutes and allow to cool.
Beat the whipped cream, sugar and vanilla sugar until stiff. Finally stir in the cream stiffener and add sour cream to the cream. Spread the cream on one base and cover with the other base.
Mix the cocoa, whipped cream and powdered sugar together and spread on the cake. Chill the cake until the icing is firm.