Wash and drain blueberries. Set aside.
Combine sugar, cornstarch, water and salt in a large sauce pan. Cook over medium heat, stirring until thoroughly combined. Add 4 cups of blueberries to the pan. (Reserve the remaining blueberries.)
Bring mixture to a boil and cook for a few minutes, stirring occasionally, until thickened.
Once the mixture has thickened, take it off the heat. Stir in the lemon juice and zest. Then, add the remaining blueberries, tossing gently to combine and coat.
Pour into a large bowl to cool. Once cool, it is ready to use or store. Fill a pre-baked piecrust or use it top your choice of cakes and desserts. Store filling in the refrigerator for up to 5 days.
*My blueberries were very sweet on their own. While we loved it exactly as is, I could have reduced the sugar by a tablespoon (which would have been a total of 8 Tablespoons or 1/2 cup) and still been quite happy with it. If you're a super sweet pie filling lover or if your berries are on the tart side, you might want to add 2 or 3 extra Tablespoons of sugar. For my family, that would be too sweet, but for others, it might be just right.
*This filling recipe is chock full of berries. If you prefer a looser filling, just reduce the berries by a cup.
*While the filling is thickened on the stove, it will set up further when it cools and even more so when it is refrigerated.
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