Whisk eggs with sugar, vanilla sugar for 2-3 minutes. In the meantime, melt the butter in the microwave for some seconds.

Once the butter is melted and cold, add it into the batter and keep whisking.

Mix the baking soda into the flour. Spoon the well-mixed content into the batter add some of the milk as well.

Keep whisking while adding flour and milk little by little at medium speed.

The batter will look thick but not too much. You will need to flour and butter your cake tray and pour the batter into it.

Wash the apples and cut them into slices. Place them on the batter creating 2-3 circles, filling the entire batter top.

Mix the powdered sugar and the cinnamon, and sprinkle on the cake. Sprinkle some vanilla sugar and put it in the oven for 40 minutes.

Use a toothpick to check whether the batter is fully cooked in the center before turning off the oven and taking the cake out.

Let it cool down before serving. Pour vanilla custard on it if you wish. (Whip the vanilla custard before using.)