Preheat the oven to 175°C top/bottom heat.
Place the eggs in a bowl and mix together with the sugar and vanilla sugar until very foamy. Add the flour and fold in by hand.
Spread the sponge on a baking tray and bake at 175°C top/bottom heat for about 20 minutes until golden brown.
Meanwhile, boil the applesauce with the custard powder until the mixture thickens. Remove the resulting apple cream from the heat.
Peel and core the two apples and cut them into small pieces. Fold them into the apple cream.
Now pour the apple cream onto the sponge cake and spread it evenly, then let it cool completely.
Finally, mix the Guma pastry cream with some cinnamon and the sugar for 3 to 4 minutes until creamy and spread it on the cooled cake.
Sprinkle with cinnamon and enjoy.