Combine blueberries and 3 tablespoons maple syrup in a medium non-stick saucepan over medium heat and bring to a low boil. Reduce heat slightly and simmer about 5 minutes, stirring frequently, or until all berries have turned dark and shiny, like little marbles. Mash with a potato masher, leaving some berries whole for texture.
Stir in chia seeds and reduce heat to low. Let simmer about 15 minutes, stirring frequently, or until thickened--it will continue to thicken in the fridge.
Remove from the heat and stir in the vanilla extract.
Recipe Notes
Keep in an airtight container in the fridge; should keep at least a week or two.