Sprinkle raspberries with lime juice and liqueur, let it steep for about 10 minutes. In the meantime, stir the quark and buttermilk until smooth. Season to taste with vanilla sugar. Peel and wash the mint leaves, cut them into fine strips or leave them whole.
Carefully fold in the raspberries and mint leaves, except some for decoration, and pour into glasses. Serve decorated with retained raspberries and mint.