First, preheat the oven. Cover the baking pan with baking paper. Beat the eggs with the sugar and vanilla sugar until creamy. Mix flour with baking powder and fold in.
Pour the batter into the baking pan. Bake in the oven at 200 °C for 25 minutes. Leave to cool.
Peel the apples, grate coarsely and mix immediately with lemon juice and sugar.
Dissolve the custard powder with 125 ml water in a saucepan. Add the apples and butter, bring to the boil briefly and then allow to cool a little.
Soak the gelatine for 5 minutes, squeeze out and stir into the warm custard-apple mixture. Allow to cool well.
As soon as the custard-apple mixture begins to gel, spread evenly on the cake base. Refrigerate for 2 hours.
Whip the cream with cream stiffener and vanilla sugar until stiff. Spread on top of the apple mixture. Sprinkle with chocolate shavings.