Whip the whipped cream with the vanilla sugar and cream stiffener until stiff and chill. Mix the quark with the natural yoghurt and the sugar until creamy. Whip the cream until stiff and fold in loosely.
Let the fruits drain, then fold in (cut the peaches or apricots into small pieces beforehand) - but then do not stir any more, otherwise the fruits will be broken.
Crumble the biscuits (e.g. in a freezer bag).
Optionally layer in dessert glasses or a large bowl. First a layer of biscuits, then quark and yoghurt cream. Finish with a layer of cookies.
The dessert should sit for a few hours - for example overnight - before serving.