Beat the butter until frothy. Add the sugar and vanilla sugar and beat everything for about 5 minutes on the highest level. Gradually add the eggs, continue beating until a frothy cream is formed. Stir in the cinnamon, flour and baking powder. Preheat the oven to 200 °. Grease the springform pan (Æ 26 cm) and dust with flour. Smooth the dough in it. Peel and quarter the apples and remove the core. Place the quarters in the dough in a circle. Bake the apple cake for about 45-60 minutes until golden brown.