Beat the whole eggs with margarine and the sugar and vanilla sugar until frothy. Stir in milk, mix in flour, baking powder and cocoa. Spread the mixture on a baking sheet lined with baking paper and bake in the preheated oven at 225 degrees for about 15 minutes. Turn the cake out onto a platter and peel off the paper. While the cake is baking, mix the juice of the sour cherries (sour cherries) with the cherry jam and the rum and stir together with the cornstarch until smooth. Boil and thicken. Spread this mixture on the hot cake and then let it cool down.
Whip the cream very stiff and stir with the sugar (you can sweeten as you like). Fold in the sour cherries up to 40 pieces and spread this cream mixture on the cake.
Sprinkle with chocolate flakes and decorate with the remaining sour cherries.