Beat the cream with the vanilla sugar until stiff. Mix the sugar, yoghurt, quark, crème fraîche with a hand mixer until the sugar has dissolved in the mixture. Then fold the whipped cream into the mixture.
Layer the cream alternately with the frozen blueberries in dessert glasses. The top layer should be cream. Garnish with the rest of the berries, chocolate shavings or brittle if you like.
Either let it steep overnight in the refrigerator or 2 hours at room temperature so that the berries thaw in the meantime.