Wash, halve and stone the plums. Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Grease the oven pan (deep baking tray; 32 x 39 cm) and dust with flour.
For the dough, whisk 200 g butter, 150 g sugar, vanilla sugar and 1 pinch of salt with the whisks of the mixer until white-creamy. Stir in 4 eggs one after the other. Mix 250 g flour, starch and baking powder and stir in briefly.
Put the dough on the fat pan and smooth it down. Spread plums loosely on top.
Mix egg yolk, 200 g sugar and 2 teaspoons cinnamon well with a fork. Pour the egg yolk-sugar mixture evenly over the plums. Bake in a hot oven for about 50 minutes.
Take out the cake and let it cool down. Cut into pieces and serve. Serve with: whipped cream with cinnamon sugar.