Warm up the milk. Put 375 g flour, 50 g butter, 50 g sugar, salt, yeast and egg in a bowl. Add the milk and work into a smooth dough using the dough hooks of the hand mixer.
Cover and leave to rise in a warm place for about 45 minutes. In the meantime, wash plums, dab dry, halve and stone them. Put the remaining flour and 60 g sugar in a bowl. Warm up the remaining fat and add it.
Mix with the whisk of the hand mixer. Knead the yeast dough again, divide into 12 equal pieces and roll out into 12 circles (12 cm Ø) on a floured work surface. Cover generously with plums and sprinkle with remaining sugar.
Sprinkle with crumble. Bake in the preheated oven (electric oven: 200 °C/ gas: level 3) for about 15 minutes.