Select the berries, wash and drain. Wash the lemon hot, dab dry and finely grate the peel. Mix quark, lemon peel, 5 tablespoons sugar and vanilla sugar. Whip cream until stiff and fold into the quark.
Put half of the quark mixture into a mould and smooth it down. Sprinkle blueberries evenly on top. Spread the cornflakes on top. Add the rest of the quark mixture and smooth it down.
Sprinkle 4 tablespoons of sugar onto the curd mixture. Caramelise briefly with a kitchen gas burner or under the hot grill of the oven until golden brown (not too long, otherwise the quark will get too warm).