4 pounds fully ripe plums (preferably sour clingstone)
1 cup water
4 cups granulated sugar
Crush plums with potato masher or food processor (do not peel or pit). Add water and bring to boil in large heavy kettle. Boil vigorously 10 minutes or until plums are tender, crushing occasionally. Ladle into jelly bag or large bowl lined with muslin towel that has been wrung out in cold water. Bring ends together, tie a loop around them and hang from hook until all juice drains out. Measure 4 cups juice into kettle. Add sugar. Stir constantly until mixture begins to boil. Boil vigorously without stirring until jelly stage (220 F on candy thermometer) or until syrup drops in a sheet from a metal spoon and is as thick as desired when tested on a cold saucer. Skim off any foam. Pour into hot sterilized jars. Seal immediately.