Use a tablespoon to press the quark through a sieve and into a bowl. Stir the natural yoghurt, vanilla sugar, lemon juice and icing sugar until smooth. Beat the cream and then, together with the sliced strawberries, stir into the quark and yoghurt mixture. Dip the ladyfingers briefly in the cloudy apple juice and place in a soufflé dish. Cover with the quark and natural yoghurt cream. Repeat this layering process two more times. Finally garnish with the sliced strawberries, leave to cool and serve as required.