In a saucepan, combine the blueberries, sugar, cornstarch, lemon juice, and salt. Stir gently to combine all the ingredients.
Place the saucepan over medium heat and cook the mixture, stirring frequently, until it starts to bubble and the sugar has dissolved. This usually takes about 5-7 minutes.
Once the mixture has come to a simmer, reduce the heat to low and continue cooking, stirring constantly, for about 5-8 minutes. The blueberries will release their juices and pop open, and the mixture will thicken to almost a syrup look.
Remove the saucepan from the heat and stir in the vanilla extract. Taste the filling and adjust the sweetness or tartness by adding more sugar or lemon juice if desired.
Allow the blueberry pie filling to cool completely before using it in your desired recipe. As it cools, the filling will continue to thicken and look like a canned version.
Use it immediately or you can store it in an airtight container in the refrigerator for up to 5 days.