Russian apple cake

Method

1. 1 Beat the sugar with the yolks, add the butter and mix well until you have a smooth batter.
2. 2 Add the rum, cocoa, baking powder, vanilla sugar, cinnamon and flour and mix everything together well.
3. 3 Last of all fold in the egg whites whisked to stiff peaks, mix well and then add the walnuts and the apples cut into cubes that are not too small (I cut the apple into 8 wedges and then cut those in half).
4. 4 Bake at 175° for about 1 hour.