For the yeast dough melt 75 g butter. Heat the milk in a small pot and dissolve the yeast in it. Mix 430 g flour, 75 g sugar, vanilla sugar and 1 pinch of salt in a mixing bowl. Add 1 egg, warm, still liquid butter and yeast milk.
Knead everything with the dough hooks of the mixer for about 10 minutes to a smooth dough. Cover and leave to rise in a warm place for about 30 minutes.
In the meantime wash, halve and stone the plums. For the frangipane, grate the marzipan roughly. Mix with 50 g butter and 2 eggs.
Line a fat pan (deep baking tray; approx. 32 x 39 cm) with baking paper. Briefly knead the dough on a little flour and roll out to a rectangle the size of the baking tray. Put the back of your hand under the dough sheet and lift the dough sheet onto the baking tray.
Press lightly all around the edge. Spread frangipane over it. Cover the yeast dough and let it rise for about 30 minutes.
Preheat the oven. (Electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Spread plums on the frangipane. Bake in the hot oven for about 25 minutes. Remove, sprinkle with approx. 4 tbsp. sugar while still warm and let cool off.