Grease a drip pan and dust it with a little flour. Wash the plums, drain them and cut them lengthways. Unfold and remove the stones.
Mix butter, 100 g sugar, vanilla sugar and a pinch of salt for approx. 5 minutes until creamy. Mix in 2 eggs one at a time. Mix the ground hazelnuts, flour and baking powder. Stir in alternately with rum and milk. Spread the dough on the drip pan and place the plums close together like a roof tile. Sprinkle with 3-4 tablespoons of sugar.
Bake the cake in the preheated oven at 175 ° C for about 25 minutes.
Beat the egg white and a pinch of salt until stiff, finally pour in 350 g of sugar. Keep beating until the sugar has dissolved. Then add lemon juice and cinnamon and beat under. Fill into a piping bag with a large star nozzle. Remove the cake and sprinkle about 18 egg white tuffs onto the cake in a spiral. Sprinkle with the nut flakes. Put it back in the hot oven and bake for about 15 minutes at the same temperature. Let cool down.