For the pork medallions with potato cap, first soak the mushrooms in a little water, then chop them. Fry in butter in a frying pan, deglaze with cream. Peel and strain the potatoes. Add mushrooms, egg yolk and chopped parsley. Season with salt, pepper and nutmeg (freshly grated), mix well and put aside.
Cut pork lung roast into 4 cm wide pieces, season with salt, pepper and thyme. Sear pork medallions briefly all around in a frying pan in a mixture of butter and oil. Remove and place on kitchen roll.
Wrap pork medallions with bacon. Place wrapped pieces of meat in a gratin dish. Using a piping bag, spread the potato mixture over the bacon-wrapped medallions. Cook for about 10 minutes in a 200 °C oven. Dissolve the drippings from the meat pan with soup and cream, boil briefly. Add the mushrooms cut into pieces and simmer.
Serve the pork medallions with the potato buns and the sauce on plates.