Drain plums, reserving juice. Pit plums; puree in a blender with juice. Transfer to a Dutch oven. Stir in the water, 1/4 cup sugar, cinnamon stick, pepper and salt. Bring to a boil. Reduce heat; cover and simmer for 10 minutes.
In a small bowl, combine cornstarch and remaining sugar; stir in cream and wine or grape juice until smooth. Gradually add to plum mixture until blended. Bring to a boil; cook and stir for 2 minutes or until thickened, stirring constantly. Remove from the heat; discard cinnamon stick. Stir in the sour cream, creme de cassis or cranberry-raspberry juice and lemon juice.
Strain half of the soup through a fine mesh strainer over a 1-1/2-qt. bowl. Repeat. Stir in lemon peel. Cover and refrigerate overnight. Garnish with sour cream if desired. Yield: 13 servings (2-1/2 quarts).