Put 400 g flour, 75 g sugar and 1 pinch of salt in a bowl. Melt 75 g fat, add milk. Stir yeast with vanillin sugar until liquid. Add lukewarm milk-fat mixture, liquid yeast and egg to the flour and knead all ingredients to a smooth dough. Cover and leave to rise in a warm place for about 30 minutes.
In the meantime, mix 250 g flour, 125 g sugar, 175 g soft fat and 1 pinch of salt with the dough hooks of the hand mixer to form crumbles. Put them in a cold place. Wash, halve and stone the plums. Knead the yeast dough well again. Grease the fat pan of the oven (38 x 32 cm) and roll out the dough. Let it rise again for about 20 minutes. Spread the plums in flakes on the dough. Put crumbles on top. Leave to rise for another 30 minutes in a warm place. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 30 minutes.
Let it rise again for about 20 minutes. Spread the plums in flakes on the dough. Put crumbles on top. Leave to rise for another 30 minutes in a warm place. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 30 minutes. Leave to cool on a rack. Serve with whipped cream