Step 1

Fill a large pot with a rack halfway full with water and bring to a boil.

Step 2

Put chopped plums into a heavy sauce pan and mash with a potato masher.

Step 3

Stir in sugar, spices, and add butter.

Step 4

Bring to a full rolling boil. Stir in pectin, returning to a full rolling boil, and continue to boil for exactly one minute, stirring constantly. Remove from heat, and skim off any foam.

Step 5

Ladle into clean jars. Wipe jar rims and threads, and cover with lids. Screw bands until finger tight.

Step 6

Put jars into pot with boiling water, on a rack. Make sure jars are covered in water. Process in gently boiling water for 10 minutes.

Step 7

Remove from water and allow jars to cool on a towel. Lids are sealed if the center does not spring back after pressing the center. (You'll hear the pops when the lids seal themselves.) If not sealed, refrigerate.