Knead a crumble dough from the ingredients margarine to baking powder. Press 2/3 of the dough into a greased springform pan (26 or 28 cm diameter). Spread the rhubarb on top, sprinkle with sugar and vanilla sugar. Then crumble the remaining crumble dough over the cake. Bake at 170 ° C in a preheated oven for 45 minutes on the 2nd rack from the bottom.