Mix the butter, sugar, vanilla sugar, salt and milk together, gradually stir in the eggs. Mix the flour and baking powder and sift over the remaining dough. Mix everything carefully and spread on a baking sheet lined with baking paper.
Cut the apples into small pieces and spread them on the bottom.
Prepare streusel from the remaining ingredients and spread on the cake.
Bake the cake at 175 ° C for about 30-35 minutes, leave to cool and dust with a little icing sugar.