Beat the eggs with the sugar and vanilla sugar in a bowl for 10 min. with a mixer. Gradually add the oil. Then the milk and finally the flour with the baking powder.
Stir with a wooden spoon. Pour it into an oven dish covered with baking paper and bake at 320°F (160 °C) for about 50 min.
For the cream:
Put the sugar and sour cream in a pot. Once it comes to a boil, add the yolks and milk. Stir until the cream thickens. Remove from the stove and add the vanilla essence and gelatin (soaked in 4 tbsp water ahead of time).
Once the layer cools, cut it into smaller layers as desired. Put the 1st layer in a form, smear it with cream, cover with the 2nd layer and smear cream generously all over the cake. Put it in the fridge to set.
Meanwhile, melt the chocolate and butter. Once the cake is cooled, decorate with the melted chocolate. Decorate as desired.