Whisk the flour, salt, and sugar in a large bowl. Cut in the cold butter until the pieces are about pea-sized. Sprinkle in the ice water slowly until the dough holds together. Divide into two discs, wrap, and chill for at least 2 hours.

In a large bowl, toss the blueberries with sugar, flour, cornstarch, cinnamon, lemon juice, and lemon zest until no dry spots remain. Lightly crush a few berries for a softer filling, if desired. Refrigerate filling for up to 24 hours.

Preheat the oven to 425°F. Roll one dough disc into a 12-inch circle, fit into a 9-inch pie dish, and set aside.

Pour the blueberry filling into the crust, spreading evenly. Dot with butter, refrigerate while preparing the top crust.

Roll the second dough disc into a 12-inch circle, cut into strips, and weave them into a lattice top. Press edges into bottom crust, trim, and flute. Brush with egg wash, sprinkle with coarse sugar, and bake at 425°F for 25 minutes.

Reduce temperature to 375°F, add a crust shield, and bake for an additional 40-50 minutes until filling bubbles and reaches about 200°F.

Let the pie cool on a wire rack for at least 4 hours before slicing. Store leftovers in the refrigerator for up to 5 days or freeze for up to 3 months.