Wash the plums
Remove the pits
Chop the plums
Place the plums in a pot
Add sugar
Add lemon juice
Stir to combine
Let the mixture sit for 15 to 30 minutes
Heat the pot over medium heat
Stir until the sugar dissolves
Bring the mixture to a boil
Reduce the heat and simmer
Stir occasionally
Skim off any foam
Cook until the jam thickens
Test the set on a chilled plate
Remove from heat
Pour into sterilized jars
Seal the jars
Let the jam cool completely