Grease the fat pan (approx. 32 x 39 cm) well. Cream butter, vanillin sugar, sugar and salt. Stir in the eggs one by one. Mix flour and baking powder, stir in alternately with yoghurt. Stir in 150 g rock candy briefly
Spread the dough evenly on the fat pan. Bake in the preheated oven (electric cooker: 175 °C/circulating air: 150 °C/gas: level 2) for approx. 25 minutes. Sprinkle with rum and let cool off
Spread plum jam on the cake. Whip cream and sour cream together until stiff, spread on top. Cut the cake into pieces. Decorate with 3 tbsp. rock candy and possibly lemon balm