Stir the quark, sour cream, lemon juice and vanillin sugar until smooth. Sprinkle icing sugar through a sieve and stir in. Chill for about 10 minutes. In the meantime, sift the blueberries, pass about 1/3 through a sieve and stir with the cassis until smooth.
Fold about half of the remaining blueberries into the quark cream. Divide the quark cream into small bowls, sprinkle with the blueberry cassis and sprinkle with the remaining blueberries. Butter waffles taste good with it.