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 and then if you want to make dump cupcakes combine 2.5 cups of filling in with 2 eggs and cake mix. Gently combine together.
Preheat oven to 350F, spray muffin tin with non stick spray. Fill 3/4 of the way full and bake for 18-20 minutes or until top springs back when touched or toothpick comes out clean.