For the apple-chocolate cake, preheat the oven to 175°C degrees. Peel the apples, remove the core and cut into wedges. Cream butter, eggs and sugar. Then add the sour cream.
Mix the flour with the baking powder, salt and cocoa and fold into the dough (it is best to sift through a sieve first). Spread the dough on a greased baking tray and cover evenly with the apples. Sprinkle the apple-chocolate cake with cinnamon-sugar and bake for 25 to 30 minutes.