Texas Tavern Burgers

1 1/2 cups chopped onion
3 tablespoons butter
1 can tomato soup
1/2 cup water
1/4 cup vinegar
2 tablespoons prepared mustard
2 tablespoons Worcestershire sauce
2 tablespoons brown sugar
2 pounds ground beef
Salt and pepper, to taste
Combine and cook onion and butter until clear and tender. Remove from fire and add remaining ingredients except beef, salt and pepper. Simmer for 10 minutes.
Cook ground beef and remaining onion until brown. Add to mixture. Salt and pepper to season.
Spread on toasted buns.
Yields 10 servings.