Add your blueberries, water, brown sugar, cinnamon, and allspice to a food processor.
Blend for 2-4 minutes, until everything is incorporated.
Serve as a part of your favorite dessert, and enjoy :)
Video
Notes
Ensure you thoroughly clean your blueberries before you add them to the food processor. Soak them for 10-20 minutes in 4 cups of cool water and 1 tablespoon of baking soda. Then, rinse the blueberries under cold water to remove any stems or leaves before blending.
Add the water to your puree a bit at a time. You don't want to add so much water that your puree becomes too liquid, but you'll want to add enough to help the blueberries break down in the food processor. If you end up with a thin puree, add more blueberries to even out the texture.
You can strain the puree through a fine mesh sieve to remove seeds and skins if you prefer a blueberry coulis with a smoother texture. This step is optional and dependent on your personal preference.