5 lbs pitted and halved plums
1/2 cup + about 1/2-2/3 cup strained freshly squeezed lemon juice (you’ll use lemon juice in two different steps)
2 1/2 lbs white cane sugar
Macerate: Place the plums in a large non-reactive container. Pour ½ cup lemon juice over the fruit and stir to combine. Then pour the sugar evenly over the fruit. Press a sheet of plastic wrap directly onto the surface of the mixture to keep the fruit from browning. Cover tightly with a lid and place in the refrigerator to macerate for (ideally) 7 days, stirring every couple days.
Taste: Remove plums from fridge and stir in 1/2 cup lemon juice. Taste for lemon flavor. If you do not detect any lemon, slowly add a little more, stirring and tasting as you go, until you can taste the tartness and lemon flavor.
Cook: Transfer the mixture to a wide, non-reactive jam pan. Bring the mixture to a boil over high heat, stirring occasionally. Cook, stirring frequently, for 4 minutes. Remove from heat. Skim and discard foam. Return to a boil, then decrease the heat slightly.
Continue to cook until the jam thickens (about 30 -40 minutes). Scrape the bottom of the pan often with your spatula, and decrease the heat gradually as more moisture cooks out of the jam. For the last 10-15 minutes of cooking, stir the jam slowly and frequently to keep it from scorching.
Test for doneness using the Freezer Test. Once a “set” is achieved, turn off the heat and do not stir. Skim any foam from the surface. Pour the jam into sterilized jars and process by canning or refrigerate.
Macerating the fruit intensifies the flavor. You can macerate for 24 hours, but the flavor will improve with longer maceration.