3 cups (about 2 lbs.) finely chopped plums
3 Tbsp powdered pectin
1/2 stick cinnamon
4-1/2 cups sugar
Grate the orange peel and reserve. Remove the white membrane from the orange and chop the pulp. Cover the peel and pulp with cold water and simmer for 10 minutes. Drain well and set aside.
Measure the plums into a heavy pan. Add the orange peel and pulp, pectin and cinnamon stick; stir well. Place on high heat and bring to a full boil, stirring constantly.
Add sugar; continue stirring and bring back to a boil. Boil hard for 2 minutes, stirring constantly. Remove from heat and skim. Remove cinnamon stick and discard.
Ladle the jam into hot, sterilized jars. Adjust lids and rings. Process in a boiling-water bath for 10 minutes. Start counting time when the water returns to a boil. Cool jars on a wire rack. Store in a cool, dark place.
Makes 4 half-pint jars.