Clean, wash and cut the leek into rings. Clean and wash mushrooms. Wash turkey breast, dab all meat dry. Cut turkey breast into 8, pork and beef fillet into 4 slices each.
Heat 1 tablespoon of oil in a frying pan. Fry the meat in it in portions on each side for about 2 minutes. Season with salt and pepper. Take out.
Heat 1 tablespoon of oil in the frying fat. Sauté the mushrooms in it for about 5 minutes. Add leek and fry for about 2 minutes. Arrange the vegetables in four small greased ramekins or a large dish.
Deglaze the frying set with 1⁄8 l cold water. Stir in sauce powder and bring to the boil while stirring. Beat butter in pieces. Pour sauce over the vegetables. Place 2 slices of turkey filet and 1 slice of beef and 1 slice of pork filet on top.
Coarsely grate the cheese and sprinkle over it. Bake in a preheated oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer) for approx. 20 minutes. Schupfnudeln are delicious with it.