Boil approximately 5 minutes, or until thickened then add blueberries and simmer 5 minutes or until a few berries have burst but most are still whole. Stir in vanilla.
Taste and add lemon zest from 1 lemon if desired for more tang.
Serve immediately for warm syrup/sauce or chill in the refrigerator in an airtight container for cheesecake topping. Blueberry Syrup will thicken as it chills.