For the crumbles, melt 150 g of fat, cool lukewarm. Mix 100 g sugar and 250 g flour. Add the fat and work into crumbles with the dough hooks of the hand mixer. Knead in the orange peel.
Chill the crumbles. In the meantime wash, halve and stone the plums. For the sponge mixture, whisk 250 g fat, 250 g sugar, salt and vanillin sugar until creamy.
Stir in the eggs one by one. Mix 200 g flour, starch and 1 packet of baking powder and stir in portions. Spread the dough evenly on a greased fat pan of the oven (32 x 39 cm).
Place the halved plums close together. Sprinkle with crumbles. Bake in the preheated oven (electric range: 200 °C/ convection oven: 175 °C/ gas: level 3) for 45-50 minutes. (Cover the cake with aluminium foil or 1 baking tray if it gets too dark!) Remove from the oven, place on a cake rack and let it cool down.
Whipped cream tastes good with it.