Drain the peaches (collect the juice), then cut into small cubes and place in a bowl. Add the frozen raspberries. Mix the low-fat quark with 4-5 tablespoons of peach juice until smooth. Whip the cream with the vanilla sugar until stiff and fold into the quark. If you like it sweeter, you can taste the mixture with sugar. Then distribute the quark mixture on the fruit and sprinkle the brown sugar over it.