Please read About Making Preserves and How to Process.

Wash, halve, and pit:

Weigh the plums and place in a bowl. Add:

If the plums are very sweet, use the lesser amount of sugar. Cover and steep.

Unless you plan to plump the preserves overnight, prepare a water-bath canner, gather all your canning equipment, place a couple of saucers in the freezer, and have ready clean, hot half-pint jars.

Transfer the plum mixture to a large heavy pot, bring to a boil, then reduce the heat and simmer until the syrup reaches the jelling point. Remove from the heat and skim off any foam. If not plumping the preserves, ladle into prepared jars, leaving ¼ inch headspace. Wipe the rims. Place lids on jars and screw on rings until fingertip-tight. Process for 10 minutes. Let cool completely and store as directed.

If plumping the preserves, the next day return them to a boil before processing and canning.