Fry the pork loin, or in Austria the pork sirloin, in hot butter on all sides until it is almost done. Let cool and rub with salt, pepper and the finely chopped rosemary.
Clean the mushrooms and cut into thin slices. First roast the chopped parsley in hot butter, then add the mushrooms, drizzle with lemon juice and finish frying until they begin to give off water.
Roll out the puff pastry to a thickness of about three millimeters, then place the ham slices on top and distribute the mushrooms on top of them. After the pork loin has been placed in the middle, fold in the dough on the sides and carefully roll everything up. Moisten the dough seam a little and seal.
Place the dough seam down on the greased baking sheet, brush the surface with the beaten egg and bake in the oven at 180 degrees for 25 minutes.