Please read Making Fruit Butters and Jellied Fruit Sauces. The method and ratios of fruit to sugar used here also work well with other tart plums, as well as with tart green apples, barely ripe quinces, cranberries, and tart blackberries. This jellied sauce is typically served turned out of the jar (like the canned cranberry sauce of Thanksgiving notoriety), sliced, and served either with a cheese plate or as a simple dessert when topped with whipped cream and toasted almonds.

Preheat the oven to 275°F. Place in a 4 ½-quart baking dish or roasting pan:

Cover and bake until simmering and syrupy, about 2 ½ hours. Let sit until cool enough to handle, then pinch the pits from the plums (discard the pits). Divide the plum pulp and juice between 2 wide, heavy 7- to 8-quart saucepans. Prepare a water-bath canner, gather all your canning equipment, and have ready 5 clean, hot half-pint jars.

Divide between the 2 saucepans:

Bring the puree to a simmer, stirring frequently, over medium heat. When the sugar dissolves, boil vigorously over medium-high heat, stirring almost constantly, until a spoon dragged over the bottom of the pan leaves a trail, 9 to 12 minutes. Ladle into the prepared jars, leaving ½ inch headspace. Wipe the rims. Place lids on jars and screw on rings until fingertip-tight. Process for 15 minutes. Let cool completely and store as directed.

To remove the sauce from the jar, run a small offset spatula or a thin, flexible knife around the inside edge of the jar, coaxing the jellied sauce away from the sides. Invert onto a serving plate, tapping gently to get the sauce to fall from the jar.