How do I do it?
Cut 12 lbs of plums in half, pit them and place in a large mixing bowl.
Drizzle with 4 cups sugar.
Using a large spoon, stir plums with sugar until all are coated
Let plums sit at room temp with the sugar for about 1 hour
Transfer plums/sugar mixture in to a large cooking pot.
Place it on the stove uncovered and bring to a boil, stirring occasionally. If it stops boiling after you stir it, continue boiling until everything is uniformly bubbling, then simmer for 10 minutes and turn off the heat. Let the pot stand uncovered until it is just warm to the touch or reaches room temp.
Transfer your boiling hot jam to the jars using a glass measuring cup and a funnel (least messy method) leaving about 1/2″ space.