Unroll the puff pastry, leaving it on the paper. Make an equal number of ½ inch wide and 2 inch long cuts (about 1.5 cm wide and 5 cm long) along both long sides. Cut out and discard the four corners, allowing the two ends to be folded in. Spread the quark filling down the middle of the pastry. Distribute the blueberry filling over the quark filling. Now, fold the two ends of pastry over the filling. Fold the pastry strips diagonally over the filling, alternating left and right. When you reach the end, cut away excess pastry about ½ inch (1 cm) longer than the strudel and fold the ends under the strudel. Use the paper to slide the strudel onto a baking sheet. Brush strudel all over with the beaten egg. Bake for about 30 minutes, until the strudel is browned and the filling is set (no longer jiggly).