Toss the meat with the mustard to coat evenly. In a Dutch oven casserole, saute the meat in very hot butter for a few minutes until meat loses its pinkness. Meat is very tender. Do not overcook. Remove meat and set aside. In the same pan, saute shallots and mushrooms in butter until mushrooms are tender. Add the wine and cook a few minutes until wine has evaporated. Add the flour and seasonings and cook for 1 minute, stirring. Add the meat to the pan, stir in the sour cream and heat through. Do not allow to boil. Serve on a bed of buttered noodles.