Add the turkey breast cutlets to a bowl. Season with pepper and salt and toss to combine. Set aside. Place a large skillet over medium heat. Add the turkey and sear until golden, for about 2 - 3 minutes per side. Transfer the meat and all the searing juices to a plate.
Add butter to the same skillet. When the butter melts, add the diced onion. Saute the onion for 5 minutes. Cut the mushrooms into thin slices and add to the skillet. Cook for 5 minutes while stirring regularly. Add the garlic and mustard. Optionally stir in the mushroom powder. Cook for a minute.
Turkey Cutlets with Mushroom Cream Sauce
Add the chicken stock and heavy cream to the mushroom sauce. Stir and bring to a boil, then simmer for 2 - 3 minutes—season with thyme, marjoram, salt, and pepper. Add the turkey cutlets with all the cooking juices. Gently push the meat into the sauce and cook for 5 minutes. Sprinkle with chopped parsley before serving. Serve with your favorite side dishes, like gnocchi, mashed potatoes, or rice.