Melt 100 g butter. Mix 500 g flour, 100 g sugar, vanilla sugar and 1 pinch of salt. Warm the milk, dissolve crumbled yeast in it while stirring. Add the liquid butter and egg to the flour mixture and work into a smooth dough.
Cover and leave to rise in a warm place for about 45 minutes.
Grease a fat pan (deep baking tray; approx. 32 x 39 cm). Wash the plums, halve them lengthwise and stone them. Knead dough on a little flour and roll out on the fat pan. Spread the plums close together, pressing them lightly into the dough.
Cover and leave to rise again for about 30 minutes. Preheat the oven (electric cooker: 200°C/circulating air: 175°C/gas: level 3).
Mix cinnamon and 75 g sugar. Spread 75 g butter in small flakes on the cake. Sprinkle with half the cinnamon sugar. Bake the cake in the hot oven on the middle shelf for about 25 minutes. Remove, sprinkle with the remaining cinnamon sugar and let it cool down.
Whipped cream.