Pour the blueberries, sweetener, lemon juice and water in a medium-sized saucepan.

Heat at a low temperature at cook it until the fruit has reduced into a sauce.

You can choose to leave the blueberries whole and make this a compote.  Or you can smash the blueberries to make the sauce thicker.  I prefer to smush them myself.

Once the sauce has fully cooked (I think it was 20 minutes at low temp for mine) I lightly sprinkle a 1/2 teaspoon of Guar Gum or Xanthan Gum to make the sauce a bit thicker.  This is an optional step.

I store the sauce in the refrigerator for up to 7 days in a closed mason jar lid.  I allow the sauce to cool completely before I put it in the refrigerator.

You can reheat the sauce when you are ready to use it again too.