Step 1

In a large bowl, toss the plums, sugar, and lemon juice.

Step 2

Cover with plastic wrap and place in the fridge overnight (or at least 8 hours).

Step 3

Place a small plate in the freezer right before cooking the plums (this is to use to check if plum jam is ready).

Step 4

Place the plum mixture in a medium sauce pan on high heat. Bring to a boil for a couple of minutes. Lower heat to a low simmer. Stir with a wooden spoon and loosen any pieces that may stick to the bottom.

Step 5

Be sure to keep stirring for about 15-20 minutes. You’ll know it’s ready when juices become thicken like a syrup. You could check temperature with a candy thermometer to make sure it’s never over 220 F. As it simmers, remove any white foam that could come to the surface.

Step 6

To make sure the jam is ready, remove the small plate from the freezer. Place a teaspoon of jam on the plate. If it sets within a minute, it is ready. If it still appears runny, return the plate to the freezer and continue to cook the plum mixture. Test again in a few minutes.

Step 7

Carefully spoon the jam into sterilized jars. Apply lids jars.

Step 8

Wipe rims with a clean, damp towel and screw lids on securely but not too tightly.

Step 9

Process in boiling water bath for 10 minutes.

Step 10

Carefully remove jars using tongs. Use potholders to tighten the lids. Place jars on a rack upside-down and let them cool. When they’ve cooled down, store them in the refrigerator. The jam should keep unopened for several months.