Make Dough: Combine flour and salt. Cut the butter into the flour using either a pastry cutter or two forks, until you reach a crumbly texture. Slowly drizzle in water while mixing until the dough can be formed into a loose ball. Divide into two equal balls, pat into disk shapes, wrap in plastic wrap, and set in the fridge to firm up for at least an hour.
Filling: Mix together your blueberries, cornstarch, sugar, lemon zest, cinnamon, and salt.
Bottom Crust: Preheat oven to 400 degrees Remove one of the pie crust disks from the fridge and roll into a large circle (at least 1 inch larger than your pie pan, I recommend a 9 inch pie pan). Transfer the crust into the pie pan, leaving ½ inch overhang on all sides.
Fill It: Spoon blueberry filling into the crust, gently evening out the top.
Top Crust: Remove the other pie crust from the fridge and roll into an equally large circle. Cut dough into 1 inch wide strips. Lay a row of dough strips going one direction (horizontal). Fold half of the strips back over themselves, then lay a strip going the other direction (vertical). Lay the horizontal strips over the vertical, then fold the other half of the horizontal strips to repeat, weaving the dough strips to form a lattice pie topping.
Bake: Brush dough with whisked egg, optionally sprinkling with a bit of sugar. Set pie in the oven, with a baking sheet below it to catch drips. Bake for 20 minutes at 400 degrees F, then reduce temperature to 350 degrees F and continue baking for 35 minutes, or until filling is bubbling at the edges. If you notice crust beginning to brown too much, cover the edges with aluminum foil.
Serve: Allow pie to cool before serving to allow blueberry filling to thicken.
*Can sub 1/2 cup tapioca starch.
Store in the fridge for 5 days, loosely covered.
To freeze, slice it into portions and store in a freezer-safe container. When ready to eat again, pop it in the oven to warm it up.