In a large pot, add blackberries, sugar, and lemon juice. Bring to a boil over medium-high heat and stir constantly until the berries are broken down and releasing their juices.

Once boiling, reduce heat to low and simmer for 15 minutes, stirring occasionally to prevent burning or sticking.

Add in pectin and stir until fully dissolved. Simmer an additional 10 minutes while stirring occasionally.

Turn off the heat and allow mixture to cool slightly before transferring it into jars or containers of your choice. Seal with lids and let rest until completely cooled before serving or storing in the refrigerator for up to 2 weeks (or in the freezer for up to 6 months).