Mix the apples with the sugar and slowly reduce 2/3 of them to half with the elderberry juice over a very low heat. Then puree with a blender.
Mix the remaining apple and sugar mixture with lemon juice, cinnamon, eggs, rapeseed oil, vanilla sugar, flour, walnuts, baking powder and apple juice.
Brush a waffle iron with rapeseed oil and gradually bake the waffles. Sprinkle these with powdered sugar and serve with the warm elderberry sauce.