In a large, heavy saucepan, melt the butter with the oil over medium heat. Add the onion, and saute until slightly caramlized, about 5 min. Add the garlic and saute another 2 min. Add all the remaining ingredients, raise the heat, and cook at a full boil for 10 min., stirring frequently. Reduce heat, partially cover, and simmer for 30 min., stirring occasionally. Sauce may be refrigerated and reheated when needed. Makes 3-4 cups.