1/4 cup cider vinegar
1/4 cup ketchup
2 tablespoons olive oil or butter
2 tablespoons soy sauce
1 tablespoon Worcestershire sauce
1 tsp. dry mustard
1 tsp. garlic powder
1 tablespoon brown sugar
1/2 tsp. onion powder
1/2 tsp. hot pepper flakes or cayenne (optional)
1 tsp. salt

Mix all ingredients together in a saucepan and bring to a boil; stir often. Cool and use right away or store in a jar in the refrigerator until ready to use.