Mix together spinach, shallots, garlic, cottage cheese, sour cream, egg and parmesan cheese; season with salt, pepper and nutmeg.
Lay out the puff pastry on a baking tray covered with greased baking paper.
Lay the filling down the middle length of the pastry sheet. Crack an egg into a cup but do not whisk it. Brush the edges of the puff pastry with egg white and close the pastry around the filling. Close the ends of the roll and carefully turn it over so that the seam is on the bottom.
Whisk what remains of the egg. Brush the strudel with it and cut a few slits in the pastry.
Bake in the preheated oven for about 30 minutes until the strudel is golden brown.