Old-fashioned plum jam requires just fresh plums and sugar, relying on the natural pectin in the fruit skins to thicken into a rich, glossy spread

Old-fashioned plum jam requires just fresh plums and sugar, relying on the natural pectin in the fruit skins to thicken into a rich, glossy spread 4 pounds fresh ripe plums (washed, pitted, and quartered; leave the skins on for natural flavor and setting power)3 to 4 cups granulated sugar (use less if your plums are naturally sweet, or up to 5 cups if they are tart)1 tablespoon fresh lemon juiceOptional: 1/2 cup water (to help start the juice-release if your plums are firm) Combine the quartered plums and sugar in a large bowl or pot. Stir well, cover, and let sit at room temperature for several hours or overnight so the natural juices release. Simmer down: Transfer the mixture to a wide, heavy-bottomed pot. Add the lemon juice and water (if using). Bring to a simmer over medium heat, stirring frequently to dissolve any remaining sugar and prevent scorching Mash and cook: Cook the mixture down for about 15 to 30 minutes, using a spoon or potato masher to break the softened plums down to your preferred texture Test the set: Place a small plate in the freezer beforehand. Spoon a tiny drop of hot jam onto the cold plate and let it rest for 2 minutes. Nudge it with your finger; if it wrinkles and doesn't run like liquid, it is ready Jar it: Ladle the hot jam into clean, dry jars, wipe the rims clean, and seal tightly. Process in a boiling water bath for 10 minutes if you want it shelf-stable for up to a year, or simply let it cool and store it in the refrigerator