In a medium saucepan, combine the blueberries, sugar, lemon juice, and salt. Mash with a potato masher or wooden spoon until the berries have released their juices.
Cook over medium-high heat, stirring occasionally, until the mixture has thickened, 18 to 25 minutes. Transfer to containers and refrigerate for up to 1 month or freeze for up to 1 year.
Excellent jam! I substituted honey for the sugar.