Mix flour, sugar and baking powder. Add little pieces of butter, egg and knead to a dough.
Form the dough in a mould. (26 cm) Pull and press slightly to fill to rim. Place in the refrigerator.
Peel and cut the rhubarb.
Mix sour cream, sugar, custard powder, egg and vanilla essence.
Put half of the rhubarb in the mould. Pour in the sour cream mixture and add the rest of rhubarb on top.
Bake in preheated oven at 200° C for the first 15 minutes. Then reduce at 180°C for another 35 minutes.
You can bake sour cream cake with any other fruits. For examples: currants, apricots, strawberries or even with apples and pears.