Mix the butter, sugar, vanilla sugar and salt until frothy. Gradually stir in the eggs well. Mix the walnuts, flour, baking powder and gingerbread spice together and fold in with the grated apples.
Pour the dough into a greased bundt cake pan and smooth it out.
Bake in the preheated oven at 180 degrees for about 60 minutes.
Dust them with a little icing sugar when they have cooled down.