Clean and wash the rhubarb and cut the stalks into 1 cm long pieces.
Make a batter from flour, cornstarch, sugar, vanilla sugar, baking powder, margarine, eggs and a little water. Spread the dough in a greased springform pan (26 cm) and distribute the rhubarb evenly on top.
For the crumble, knead the whole wheat flour with 80 g sugar and 80 g butter. Then distribute it evenly on the cake.
Bake in the preheated oven at 150 ° C for approx. 80 minutes. Then remove from the springform pan.
Tip: When the rhubarb season is over, the cake also tastes good with other fruit. We like to make it with apricots. With apples you don`t need crumble, just a lot of fruit.