Preheat the oven for 180°C.
Cream butter, sugar, and vanilla sugar in a mixing bowl.Add the eggs one at a time and whisk together.
Sift in the flour and baking powder. Add the ground almonds.
At last, add the liquid ingredients (lemon juice and milk) and whisk to get a smooth batter.
Grease a silicone cake mould and pour the batter in.
Peel the apples, cut into quarters and remove the insides.
Cut into the quarters but not all the way through so that the slices stay together.
Place as many apple quarters on the cake as possible!
Bake for about 40 minutes until beautifully golden. Served with whipped cream.