Melt the butter and let it cool. Mix butter, sugar, eggs, flour, baking powder, cinnamon, ground hazelnuts, water and vanilla sugar in a bowl and then add the peeled and chopped apples.
Pour the mixture into prepared muffin tins, approx. 1.5 tablespoon per tin. Bake at 180 degrees top / bottom heat in a preheated oven for about 20 minutes.
Tip: At 3/4 of the baking time, sprinkle the muffins with slivers of almonds and finish baking.
Let it cool down and sprinkle some powdered sugar over it.