Mix the butter with the sifted sugar, vanilla sugar, cinnamon and rum until frothy. Gradually stir in the egg yolks. Mix the flour and baking powder, sieve and add to the yolk. Add the cream.
Beat egg whites into snow and fold in. Stir the plums into the batter.
Butter, flour and sprinkle with flaked almonds. Pour half of the batter into the mold and spread some liquid caramel syrup on top. Pour in the rest of the batter and spread some more liquid caramel syrup over it. Loosely pull the dough through with a fork.
Bake in the preheated oven at 180 ° C for about 60 minutes.