Preheat oven to 350°F (180°C).

Using a mixer, cream the butter until smooth. Gradually add sugar and vanilla sugar and mix until sugar is absorbed by butter. Add eggs, one at a time, waiting until egg is completely absorbed before adding the next one. If eggs scramble a bit, add a little flour to help butter absorb eggs.

Cut up the Marzipan into small pieces and add to butter-egg mixture. Mix until the marzipan has been fully incorporated into the butter-egg mixture.

Add flour, cinnamon, baking powder, and ground hazelnuts.

Wash, peel, core, and slice apples.

Grease a Springform pan. Pour batter into pan. Spread batter evenly throughout the pan. Arrange apple slices onto top of cake batter, pressing slices slightly into batter.

Mix teaspoon of sugar with a pinch of cinnamon. Sprinkle over apples.

Bake cake for 60 minutes, or until toothpick poked into center of cake comes out clean.

Allow cake to cool completely. Dust with powdered sugar.