Simmer onions in butter, stirring often. Cook until golden. Sprinkle in flour and blend thoroughly. Add wine vinegar, beef stock, and tomato paste. Season with salt and pepper and touch of garlic and simmer 20 minutes. Pour half sauce in bottom of baking dish. Add meat and cover with rest of sauce. Sprinkle with bread crumbs and Parmesan cheese. Bake at 350 degrees F until heated through.