Heat oven to 425 degrees (400 if you have a convection oven). Take one crust out of the fridge. Give it about 10 minutes before you try to roll it out, or unroll it if it is a premade rolled crust.
Place the crust into bottom of 9-inch pan. Trim any excess hanging over the edge. Place in the refrigerator while you complete the rest of the steps. If you have a premade crust, then take the second one out of the fridge to get the chill off so you can easily place it over the blueberries to top the pie, or cut into a lattice if you desire.
In a large bowl, mix blueberries, lemon zest, lemon juice, thickener, sugar, cinnamon, and a pinch of salt in a bowl. Gently mix to combine. Pour into pie panand evenly distribute.
In a small bowl, mix egg and water.
Place second crust on top (or follow the YouTube instructions above to make a lattice crust). Crimp edges. Cut 2-4 slits in the top if crust covers the entire top. Brush all exposed pastry with the egg wash. Sprinkle with sugar.
Place on a baking sheet covered with foil.
Bake at 425 or 400 for 20 minutes. Reduce heat to 350 degrees and bake another 30 to 40 minutes (or longer) until the blueberries are bubbling. If the crust begins to brown too quickly, cover with foil part way through baking.
Sometimes I start with the pie covered – very loosely with foil – and then take the foil off for the last 30 minutes.