This is the recipe for Memphis Magic sauce from Cheryl and Bill Jamison's Smoke and Spice: Cooking with Smoke, the Real Way to Barbecue. This is my favorite book on barbecue. If you're only going to own one book on the subject, I think this should be it.
3 Tbsp butter, preferably unsalted
1/4 cup minced onion
1 cup white vinegar
1 cup tomato sauce
1/4 cup Worcestershire sauce
2 tsp sugar
1 tsp salt
1/2 tsp ground black pepper
1/8 tsp cayenne pepper
Dash of Tabasco or other hot pepper sauce
Melt the butter in a saucepan over medium heat. Add the onions and sauté until they begin to turn golden. Stir in the remaining ingredients, reduce heat to low, and cook for approximately 20 minutes. If you want the sauce thicker, cook longer. Keeps well in the refrigerator. Freezes well, too.