Sterilize enough jars or plastic containers with tight-fitting lids to hold 6 1/2 cups (1.625 L) jam. Remove plum pits. Finely chop plums in a food processor. Place in a saucepan with 1/4 cup (75 mL) water. Bring to a boil. Stir often. Reduce heat, cover and simmer 5 minutes. Place 3 cups (750 mL) in a large bowl and stir in peel and sugar just until mixed. Let stand 10 minutes.
In a small saucepan, stir remaining 3/4 cup (175 mL) water with fruit pectin crystals. Bring to a boil, stirring often. Boil 1 minute, stirring constantly. Stir into fruit mixture. Continue stirring 3 minutes. A few sugar crystals may remain. Immediately pour or spoon into sterilized jars or containers, leaving about 1/4-inch (0.5-cm) headspace for expansion. Cover with lids. Let stand at room temperature until set, up to 24 hours. Refrigerate 2 to 3 weeks or freeze up to 1 year.
Nutrition (per serving)
A slathering of this jam is delicious on toast or as a zesty pork glaze.