1 (15 oz.) can tomato sauce
1/2 c. light brown sugar
1/4 c. vinegar
2 tsp. prepared mustard
2 1/2 lb. ground chuck
2 eggs, slightly beaten
1/2 c. diced onion
1/2 c. fine dry bread crumbs
2 tsp. salt
1 tsp. pepper

Mix tomato sauce, sugar, vinegar, and mustard together. Mix remaining ingredients with 1 cup of tomato mixture. Make into a loaf pan. Pour 1/4 cup tomato mixture over top and bake at 375 degrees for about 1 hour. Heat remaining sauce to serve over meatloaf slices.