For the dough, knead all ingredients and roll out on a prepared baking sheet. For the curd mixture, cream butter with icing sugar and vanilla sugar, slowly beat in eggs. Add the vanilla pudding powder, lemon juice and curd and mix well. Spread the curd mixture on the prepared dough and bake in the preheated oven at 200 °C for about 30 minutes.
For the topping mix sour cream with egg, vanilla pudding powder and oat flakes well, then add the currant and mix well. Spread the mixture on the pre-baked cake and bake for about 15 minutes until done.
Serve the cake sprinkled with icing sugar.