Place the plums in a blender or food processor. Add the water and mix at high speed until the plums are pureed. Pour the puree into a 1-quart saucepan. Add the remaining ingredients and simmer over low heat for 20 minutes to reduce the sauce. If necessary, add cornstarch to thicken the sauce.
Remove from heat. Add sugar, to taste. Serve hot or cold.
Recipe courtesy of Ritz Carlton Rose Hall Resort, St. James, Jamaica