2 rolled-out rounds basic pie dough
4 cups blueberries
1 tbsp. fresh lemon juice
¾ cup sugar
3 tbsp. cornstarch
½ tsp. finely grated lemon zest
¼ tsp. salt
¼ tsp. cinnamon
1 tbsp. cold unsalted butter, cut into pieces
1 tbsp. water
Line the bottom of a 9-inch pie pan with one of the rolled-out dough rounds. Set pan aside in a cool place until ready to fill.
To make the filling, place the blueberries in a large bowl, sprinkle with the lemon juice and toss to coat evenly. In a small bowl, stir together the sugar, cornstarch, lemon zest, salt and cinnamon. Sprinkle the sugar mixture over the berries and toss to distribute evenly. Immediately transfer to the dough-lined pan. Dot with butter pieces. Place the remaining dough round on top of the pie and trim the excess from the bottom and top rounds. Crimp the dough rounds together to seal the edges. Be sure to cut vents in the top crust to allow steam to escape during baking.
Refrigerate the pie until the dough is firm, 20-30 minutes. Position a rack in the lower third of the oven and preheat to 375°. In a small bowl beat the egg and water with a fork to make an egg wash. Brush onto the top crust just before baking.
Bake the pie until the crust is golden and the filling is thick and bubbling, 50-60 minutes. Transfer to a wire rack and let cool completely to set, 1 to 2 hours. Serve at room temperature or rewarm in a 350° oven for 10 to 15 minutes just before serving.
Note: If fresh blueberries are unavailable, use frozen blueberries (without thawing) and increase the baking time by 10-15 minutes.