Thaw the puff pastry and spread it out on a surface sprinkled with flour. Prepare the filling by mixing the cottage cheese, sugar, lemon zest and lemon juice well. Spread the cottage cheese mixture along the length of the puff pastry and a little off to the sides.
Arrange the halved apricots or peaches on the cottage cheese. Fold the two ends of the puff pastry inward so that one end completely covers the filling and the other end sits atop the middle of the first.
Spread the top with beaten egg. Bake the cake in a very hot 428°F (220 °C) oven. Cut the cake once it is well baked.