In a saucepan over medium heat, place all ingredient for the syrup together (except for the vanilla extract).
Whisk the mixture together and bring it to a simmer for about 10 minutes.
About 3 minutes in, once blueberries soften a little, use an immersion blender to blend up the mixture. Hot mixture can splash, so make sure you’re using a saucepan with high sides.
After about 10 minutes of simmering, cut the heat, add in the vanilla and strain the syrup into a jar or glass container with a lid.