Add sugar, blueberries, and lemon juice to a sauce pan, and slowly heat until boiling, stirring constantly.
Pour in liquid pectin and stir until combined.
Lower to a simmer and continue stirring until reaching desired consistency (mixture should coat a wooden spoon).
Notes
You can easily increase or decrease this recipe depending on the amount of blueberries you have on hand. You can also adjust the sweetness if you like your sauce more or less sweet or tart. Simply taste it after adding the sugar/lemon juice and add more if desired. The pectin will not affect the taste.