Combine all ingredients in a pot and simmer until plums are very soft, about 15 to 20 minutes. Remove cinnamon stick and allow to cool. Pour into a blender or food processor and blend until smooth. Use immediately or refrigerate for up to a week.
Recipe by Ultimate BBQ Sauce Recipes! at http://www.bbq-sauce-recipes.com/fruit-based-bbq-sauces/258/plum-bbq-sauce/