Fill the mason jars with the pumpkin puree and leave at least a 1-inch headspace for expansion. If your jars have shoulders, do not fill above the shoulders.
Refrigerate the jars to chill them before freezing.
Transfer the cold jars to the freezer and freeze until you need them. They'll last well for approximately 6 months in mason jars or longer in vacuum sealed bags.
Thaw the frozen pumpkin in the fridge before using.