Preheat oven to 250°. Place pork tenderloin pieces between sheets of waxed paper and flatten to a thickness of 1/4 - 1/2 inch. Combine flour, salt and pepper. Dredge medallions in seasoned flour. In a large skillet, heat butter over medium-high heat. Saute medallions for 2-3 minutes on each side. Remove to a baking dish (12x8) and cover to keep warm. Add wine vinegar and pepper to skillet and boil to reduce by 2/3. Add cream and mustard and simmer the mixture for 5 minutes or until it begins to thicken. Pour liquid over pork medallions and bake, uncovered, for 1 hour at 250°. Baste meat occasionally with sauce. Sprinkle with chopped parsley. 4-6 servings.