Place 1 cup of water and sugar into a medium size saucepan and turn the heat on medium high. Stir to combine and add 1 cup of the blueberries. Increase the heat to high and bring to a boil. *If you are using fresh blueberries, let the mixture boil for 1-2 minutes so the blueberries release their juice. You can go by the color of the syrup and when it is a dark purple you are ready to add the cornstarch slurry and finish the pie filling.
Combine 3 Tablespoons of cornstarch with 3 Tablespoons of water in a small bowl and stir until smooth and free of lumps.
Reduce the heat to medium and mix in the cornstarch slurry, stirring constantly as it thickens. The mixture might turn a cloudy light color, just keep stirring and let it cook a minute or so and it will turn very shiny and deep purple.
Turn off the heat, add the remaining blueberries and lemon juice. Stir to combine. You can use the filling right away, or place it in an airtight container and refrigerate it until use.
Nutritional Values are for the entire batch of pie filling.Yield: 3 cups of blueberry pie filling. If you want to serve the blueberry filling warm, reheat it over low heat on the stove.If it is too thick after chilling, add a teaspoon of water at a time and stir until it reaches your desired consistency.If the mixture looks cloudy or very light in color after refrigerating, either too much cornstarch was used, or it simmered too long, reducing the water too much. It's an easy fix, though. Simply reheat the pie filling over medium heat, add about a Tablespoon of water, and stir. Let simmer for a few minutes.