Before: Make your pie crusts & let them rest in the fridge 30 minutes. Or if you made them overnight, pull them out on the counter while we do the rest.
Preheat Oven to 400°
Start Filling: In a large bowl, add blueberries & 1 cup sugar. Toss until coated. In a small bowl, add 2 teaspoon vanilla extract, 2tbs lemon juice and 3tbs cornstarch. Stir together until no clumps remain. Pour over sugared blueberries and toss until everything is coated well. Set bowl of blueberry filling to the side.
Roll out Crust: Roll out your pie crusts and place first one into 9inch pie dish. When oven is preheated, add blueberries to pie dish inside crust. Spread blueberries evenly. Cover the top with your second crust and crimp edges. Be sure to cut two small slits in the center.**
Bake: Beat egg in small dish and brush over all visible pie before baking. Place in oven and bake 35-45 minutes. Blueberries should be bubbling & crust will be golden brown. Remove from oven & let cool completely to set. You can serve warm (with ice cream of course!, but it will be runnier)