Grease the fat pan (approx. 32 x 39 cm; at least 3 cm deep). For the crumbles, melt butter at low heat. Mix flour, baking powder, sugar and 1 pinch of salt in a bowl. Add 2 eggs. Gradually knead the liquid butter into the mixture with a hand mixer
Spread approx. 2/3 of the crumble as a base on the fat pan and press on. Mix sour cream, 2 eggs and vanilla sugar. Spread on the crumble base. Spread plum puree in thick splodges on top. Sprinkle the rest of the crumbles over it
Bake in the preheated oven (electric cooker: 200 °C/circulating air: 175 °C/gas: level 3) for approx. 30 minutes. Let them cool down. Cut the cake into triangles and dust thickly with icing sugar