Mix together beef, bread crumbs, salt, pepper and eggs. Add onion and half of the tomato sauce. Form into a loaf in a 9-in x 5-in x 3-in pan. Bake at 350F for 50 minutes. In saucepan, combine sugars, vinegar, mustard and remaining tomato sauce. Bring to a boil. Pour over meat loaf; bake 10 minutes more.
YIELD: 6 servings