In a large pot, combine the blueberries, sugar, and lemon juice. Stir well to combine.

Heat the mixture over medium heat, stirring frequently until the blueberries start to break down and release their juices.

Once the mixture is bubbling, reduce the heat and let it simmer for about 30 minutes, stirring occasionally.

If using pectin, add it according to package instructions during the last 5 minutes of cooking.

Remove from heat and let the jam cool slightly before transferring to sterilized jars.

Seal the jars and let them cool completely at room temperature before refrigerating.