For the Filet Wellington, salt and pepper the pork lung roast and sear well on all sides in a pan. Remove from the pan and wrap in aluminum foil.
Slice the leeks and roast them in the pan. Add the cleaned and chopped mushrooms and roast well. Let cool briefly and stir in crème fraiche, salt, pepper and chopped parsley.
Roll out the puff pastry. Spread the mushroom mixture evenly on it, leaving some free space on all sides.
Remove the pork lung roast from the aluminum foil, wrap it all around with bacon and place it on the mushroom mixture – fold in the side edges, roll everything up and brush with egg.
Bake in the preheated oven at 180 °C for approx. 25 min.