Warm the milk and melt the butter in it. Sift the flour into a bowl and mix with the yeast, sugar, vanilla sugar and salt. Add egg and milk-fat mixture. Process with a hand mixer (dough hook) to a smooth dough. Cover the dough and let it rise until it has visibly enlarged (approx. 20 minutes).
In the meantime, wash the plums, remove the stems, stone and halve.
Process the ingredients for the crumble with the hand mixer (whisk) to make crumble.
Knead the yeast dough on a lightly floured surface and roll it out in a pan (baking sheet). Cover the dough with prunes like a roof tile. Spread the streusel evenly on top. Let it go again until it has visibly enlarged (about 20 minutes). Then put the cake in the preheated oven.
Top / bottom heat: 200 degrees
Hot air: 180 degrees
Baking time: 25-30 minutes
Then let the cake cool in the drip pan on a wire rack.