For the filling made of milk, sugar and custard powder, cook a vanilla pudding. Then stir in the sour cream and let the cream cool down a little, stirring again and again.
For the dough, beat the butter / margarine until frothy, stir in the sugar and vanilla sugar and keep beating until the sugar is well dissolved. Stir in the eggs one at a time for half a minute. Mix the flour with the baking powder and finally stir in with milk.
Pour the dough into a greased springform pan (26 cm diameter). Place the currants on top (put frozen berries on top) and then spread the pudding and sour cream mixture on top.
Preheat the oven to 180 ° C top / bottom heat.
Make crumbles from butter, sugar, flour and desiccated coconut and sprinkle over the pudding and sour cream mixture.
Bake the cake for about 40 minutes (test with chopsticks!). Let the cake cool down, remove it from the mold and sprinkle with powdered sugar if necessary.