For the filling, remove the skin from the sausage. Chop the sausage finely. Peel onion, dice very finely. Clean the mushrooms, wash if necessary and dice 100 g very finely. Put the rest of the mushrooms aside. Wash thyme, dab dry, remove leaves and chop.
Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Heat 1 tablespoon of oil in a pan. Brown the mushroom cubes in it. Add sausage and onion and fry for 1-2 minutes. Remove from the heat.
Stir in the thyme. Season with pepper, let it cool down a bit. Stir in breadcrumbs and egg yolk.
Wash the meat and dab dry. Cut a deep pocket into each cutlet. Press the filling well into it. Stick with wooden skewers. Heat 2 tablespoons of oil. Brown the chops on each side.
Season with salt and pepper. Place in an ovenproof dish and bake in a hot oven for 15-20 minutes. Set the pan with the frying fat aside.
In the meantime cut the remaining mushrooms into slices. Heat frying fat in a pan. Sauté the mushrooms well in it. Dust with flour and sauté briefly while stirring. Deglaze with sherry, cream and 150 ml water.
Bring to the boil and simmer for about 5 minutes. Season to taste with salt and pepper. Cut chops in half if necessary and arrange. Add the sauce. Served with mashed potatoes.