Thanks to Tracy at Sugarcrafter.net for this delicious recipe!
Run the plums through your food processor. In a large sauce pan, combine plums, water, lemon juice, and spices. Working in batches, run the plum mixture through your food mill. Measure 3-4 cups plum purée. Return to the sauce pan and stir in the sugar. Bring to a boil over medium-high heat, stirring frequently. Reduce heat and boil gently until mixture thickens and holds its shape on a spoon. Prepare your canning supplies; sterilize the canning jars by running them in almost boiling water for several minutes, and boil a few cups of water in a small saucepan for the lids. Ladle hot butter into hot jars, leaving 1/4″headspace. Wipe rim and center lids on jars, and then screw down bands just until resistance is met. Place jars in canner, ensuring they are covered with water, and boil for 10 minutes. Remove canner lid and wait 5 more minutes before removing jars.