Let the blueberries thaw and take the puff pastry out of the fridge. Preheat the oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Beat egg white and sugar with the whisks of the mixer until slightly stiff. Stir in the quark. Mix berries and jam.
Unroll puff pastry together with baking paper. Cut approx. 5 cm deep into the long sides at a distance of 2 cm. Spread the quark mixture on the middle strip of dough. Spread the blueberry mixture on top.
Fold the cut dough strips of the left and right long side alternately at a slight angle to the middle over the filling. Pull the paper onto a baking tray. Bake in a hot oven for 20-30 minutes. Remove from the oven and allow to cool briefly.
Mix icing sugar and 2 tablespoons of water. Dribble the icing over the cake.