Preheat the oven to 218°C. On a lightly floured surface, roll one disk of pie dough into a 13-inch circle. Place the flattened dough in a 9-inch pie pan and let the excess pie dough hang over the edges.

In a large bowl, combine the blueberries, lemon zest, and lemon juice, tossing them until combined.

Add the sugar, cornstarch, cinnamon, and salt to the bowl of blueberries.

Stir until the berries are well coated in the sugar mixture.

Pour the filling into the pie crust and gently pat it out into an even layer.

Dot the cubes of butter all over the top of the filling, distributing it evenly.

Roll the remaining pie crust into a 12-inch circle. Cut the dough into 10-12 strips, about 1-inch wide, using a pastry wheel or knife. Arrange the strips on top of the pie in a lattice top pattern by weaving the strips over and under one another. Trim the excess dough so there is about 1 inch of overhang from the edge of the pie dish. Tuck the excess dough under itself and crimp the edge with your fingers to seal the dough.

Lightly brush the pie crust with the egg wash, and sprinkle with more sugar if desired. Place the pie on a rimmed baking sheet and bake for 20 minutes. Reduce the oven temperature to 175°C and continue baking for 35-45 minutes, or until the crust is a deep golden brown and the filling is bubbling around the edges. Let the pie cool completely before slicing or for about 4 hours.