Season the meat with a little salt and pepper and fry briefly and vigorously in a pan together with a diced onion.
Then deglaze with water and remove from the heat. Chop the second onion, mix with the mustard and ketchup to make a marinade. Cut the meat in half from the top (as if sliced) and spread the marinade between the slices.
Place the roast in a roasting pan, add the gravy and cook covered in the oven at 180 degrees for one hour. Then mix the whipped cream and sour cream, add to the roaster and braise everything open for another 10-15 minutes.
Season the sauce to taste before serving. Serve with fried potatoes and salad.
