Remove the stones from the plums and cut them into quarters.
Preheat the oven to 180 °C. Melt the butter for the dough and then beat with the sugar until fluffy.
Separate the eggs and beat the egg whites until stiff. Mix the yolks with the butter-sugar mixture and beat again, stir in the remaining ingredients. Fold in the beaten egg whites last. Spread the dough on a baking tray and cover with the plums. For the crumble, knead all the ingredients together and then crumble.
Spread the crumble on the cake and bake the cake for about 40 minutes. This cake can of course also be baked with any other fruit.