Chill your tools and crust: Keep the dough cold. If using homemade, chill disks at least 1 hour. Cold dough = flaky layers. Science!
Preheat the oven: Set to 425°F (220°C). Place a rack in the lower third and put a rimmed baking sheet on it to preheat and catch drips.
Make the filling: In a large bowl, combine blueberries, sugar, cornstarch, lemon zest, lemon juice, salt, and cinnamon (if using). Toss gently until evenly coated. Let it sit 10 minutes so the cornstarch hydrates.
Roll out the bottom crust: On a lightly floured surface, roll a dough disk to a 12-inch circle. Fit into a 9-inch pie dish, letting excess hang over the edge. Chill for 10 minutes.
Fill it up: Spoon the blueberry mixture into the crust, including any juices. Dot with butter cubes.
Top crust time: Roll the second disk to an 11–12-inch circle. Lay over the filling.Trim excess, leaving about 1 inch overhang. Fold edges under and crimp firmly. Vent and shine: Cut 4–6 slits in the top (or make a lattice if you’re feeling extra). Brush with egg wash and sprinkle coarse sugar.
Bake hot and fast: Place the pie on the preheated baking sheet.Bake at 425°F for 20 minutes to set the crust. Lower the heat: Reduce to 375°F (190°C) and bake 35–45 minutes more. You want a deeply golden top and thick, bubbly juices visible through vents.
Shield if needed: If edges brown too quickly, tent with foil or use a pie shield for the last 20 minutes.
Cool properly (seriously): Let cool at least 3–4 hours on a rack. The filling continues to set as it cools.Cutting early = blueberry landslide. Serve: Slice with a sharp knife. Great at room temp or slightly warm. Add vanilla ice cream or whipped cream because you deserve it.