Place the blueberries, sweetener, and salt in a small saucepan and stir to combine. Bring the mixture to a boil, while whisking. The blueberries will begin to release their juices. Reduce the heat to a simmer, and allow the mixture to cook for 5 minutes, checking in to give it a stir every minute. Some of the blueberries will pop as they cook, releasing more juices.
In a small dish, whisk the water and cornstarch until dissolved. Whisk the mixture into the blueberry sauce. Bring the sauce back to a low boil, and allow it to boil for 2 minutes, while whisking. It should thicken up nicely.
Remove from the heat and whisk in the lemon juice and vanilla extract. Let the sauce cool for a few minutes before serving.
Recipe by Go Dairy Free at https://www.godairyfree.org/recipes/chunky-maple-blueberry-sauce