Melt the butter in a skillet over medium heat. Stir in the onion and cook it until tender. Meanwhile in a medium bowl, mix together the remaining ingredients. Add this to the cooked onions and bring to a boil. Then reduce heat to low and simmer for 30 minutes, stirring occasionally. Use immediately as a grilling sauce. This also keep well for two weeks in the refrigerator. Great on chicken, pork and beef. Very tasty and worth the time!