Whisk all ingredients together in a non-reactive saucepan. Turn heat to medium-high and allow the sauce to just come to a boil.
Lower heat, cover, and simmer for 15-20 minutes, or longer.
Taste and add a vinegar if needed, and salt and pepper, to taste.
Transfer to a large jar. Cover and refrigerate until ready to use.
This recipe calls for tamarind paste which is made from the tropical tamarind fruit. It can be found in well-stocked grocery stores in the ethnic foods section, Asian, or Indian markets. It has a tangy, rich flavor. It can be omitted or substituted with 2 tablespoons ketchup plus 1 tablespoon Worcestershire sauce, or 11/2 tablespoons brown sugar plus 11/2 tablespoons vinegar or citrus juice.
You can make your own BBQ sauce or use your favorite brand. Place them in the slow cooker covered with sauce. Once warm, turn down to low and enjoy!