In a saucepan over medium heat, add blueberries, water, sugar, lemon juice and salt. Bring to a simmer, stirring frequently.
Add the cornstarch paste and gently stir until combined. Continue cooking berry mixture until thickened, about 5 to 7 minutes. The sauce should coat the back of a spoon.
Remove from heat and stir in the vanilla. Serve warm, room temperature or chilled.
Notes
Store in an airtight container in the refrigerator for up to 2 weeks.Frozen berries may also be used (do not defrost). Reduce water to 1/3 cup and add more, 1 tablespoon at a time, if a thinner sauce is desired.