Remove skins from plums by dipping in boiling water for 1 minute or until skin breaks; cool immediately by dipping in ice water or running under cold tap water. Remove pits and discard. *Note: This is an optional step but yields a more professional result. (Skins may be left on if you don't mind them).
Combine all ingredients in a blender; process until smooth. In a heavy bottomed saucepan, bring to a boil. Reduce heat to very low and simmer for about 10 minutes.
Use sauce for basting or serve as an accompaniment for dipping.