Rinse five 1-cup plastic or freezer-safe containers and lids with boiling water. Dry thoroughly. Mash blueberries; transfer to a Dutch oven. Add lemon juice; stir in pectin. Bring to a full rolling boil over high heat, stirring constantly.
Stir in sugar; return to a full rolling boil. Boil for 1 minute, stirring constantly. Remove from the heat; skim off foam. Ladle into containers and cool to room temperature, about 1 hour.
Cover and let stand overnight or until set, but not longer than 24 hours. Refrigerate for up to 3 weeks or freeze for up to 12 months.
If using frozen blueberries, use without thawing to avoid discoloring the batter.