Prepare the crust: Preheat oven to 425°F. Place a baking sheet inside to heat. Roll the bottom crust into a 9-inch pie pan, press gently into place, and chill if the dough feels soft.
Mix the filling: In a large bowl, toss blueberries with sugar, cornstarch, lemon juice, lemon zest, cinnamon, and salt until evenly coated.
Fill the pie: Pour the blueberry filling into the crust, mound it slightly in the center, and dot the top with small pieces of butter.
Add the top crust: Cover with a lattice crust or full top crust. If using a full crust, cut 4–6 small steam vents. Trim and crimp the edges.
Brush and sprinkle: Brush the top lightly with egg wash, then sprinkle with coarse sugar if desired.
Bake: Bake at 425°F for 15 minutes. Reduce heat to 375°F and bake 40–50 minutes more, until the crust is golden and the filling bubbles in the center. Cover edges with foil if needed.
Cool: Let the pie cool for 2–3 hours before slicing so the filling can set cleanly.
