For the plum cake, cut the plums in half and remove the seeds.
Cream butter with powdered sugar and vanilla sugar. Add the egg yolks, salt and cinnamon and mix well. Whisk QimiQ until smooth and stir into the mixture.
Mix flour with baking powder and add three quarters of it to the mixture.
Prepare a beaten egg white from the egg whites. Fold the beaten egg whites into the mixture with the remaining flour. Spread the dough on a baking sheet and cover with the halved plums.
Put the plum cake into the preheated oven and bake at 200°C for about 20-30 minutes.
Serve while still warm sprinkled with a cinnamon-dusted sugar mixture.