Mix the flour and sugar and knead with the egg and butter to form a dough.
Shape into a ball, wrap in cling film and refrigerate for about 30 minutes.
Wash the rhubarb thoroughly and cut into 2 cm pieces.
For the filling, mix the sour cream with the eggs, sugar and custard powder until smooth.
Take the dough out of the refrigerator and press it flat into a springform pan, forming a small edge all around.
Spread the rhubarb pieces on top and then spread the sour cream mixture on top.
Bake in a preheated oven at 175 ° top / bottom heat for about 50 minutes.
Let the cake cool down well before serving so that the pieces can be cut more easily. And then --- enjoy!