Fry the schnitzel in clarified butter for about 4 minutes on each side and then place in an ovenproof saucepan with a lid. Cut the onion into small pieces and sauté until translucent. Add the diced ham and mushrooms. Stir in the cream and pour everything over the schnitzel. Cover everything and leave to stand for about 12 hours.
Then cook in the oven at medium heat (around 180 degrees) for 1 hour.