For the crumbles, melt 120 g butter. Put 200 g flour, 70 g sugar and cinnamon in a bowl and mix. Add butter and knead into crumbles using the dough hooks of the hand mixer.
Chill the crumbles. Wash, halve and stone the plums. Cut 200 g butter into pieces. Cream 200 g sugar, butter and vanilla sugar with the whisk of the hand mixer. Stir in the eggs one by one.
Mix 400 g flour and baking powder and stir in alternately with the milk. Spread the dough on a greased fat pan and cover it tightly with plum halves. Spread the crumbles on the cake and bake in a preheated oven (electric range: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 50 minutes.
Remove and let it cool down. Cut the cake into pieces. Whipped cream tastes good with it.