Meatloaf with Sweet and Sour Sauce

1-8 oz can tomato sauce
1/4 C brown sugar, packed
1/4 C cider vinegar
1 tsp prepared mustard
1 egg, slightly beaten
1 onion, minced
2 stalks celery, chopped
1/2 green pepper, chopped
1/4 C Italian seasoned breadcrumbs or crushed crackers
2 lb ground sirloin
1/2 tsp salt
1/4 tsp black pepper

In a saucepan mix tomato sauce, brown sugar, vinegar, and mustard. Cook until sugar is dissolved. Set aside. Take onion, celery, green pepper, and one tablespoon water; put in bowl. Put Saran wrap over them and put in microwave to soften. Combine egg with vegetables (celery, onion, green pepper), crackers, salt, black pepper, meat and 1/2 cup tomato sauce mixture. Mix thoroughly. Shape into loaf. Put into baking dish and pour remaining tomato sauce mixture over meatloaf. Bake covered at 350 degrees for one hour. Baste occasionally. If sauce thickens, add 1/4 cup water to sauce. Serve sauce separately.