Select the blueberries, wash and drain well. Wash lemon hot and dab dry. Grate the peel thinly, squeeze the lemon.
Mix quark with lemon juice and zest, sugar and vanilla sugar. Whip the cream until stiff, allowing the cream setting agent to trickle in. Fold into the quark.
Put half the cream quark in a flat dish (approx. 1.2 l capacity) and smooth it down. Spread blueberries evenly on top. Sprinkle with cornflakes and spread the rest of the cream quark on top.
Sprinkle brown sugar on the cream and chill everything for about 30 minutes. Or caramelise the sugar with a gas burner until golden brown.