Prepare Crust. In a large mixing bowl, combine flour, salt, and sugar. Add cold, cubed butter and cut it into the flour mixture using a pastry cutter or your hands until the mixture resembles coarse crumbs. Gradually add ice water, one tablespoon at a time, until the dough comes together. Divide the dough into two discs, wrap in plastic wrap, and refrigerate for at least 1 hour.
Preheat Oven. Preheat the oven to 375°F (190°C).
Prepare Filling. In a large bowl, combine the blueberries, sugar, cornstarch, lemon juice, lemon zest, cinnamon, and vanilla extract. Gently toss to mix evenly.
Roll Out Dough. On a lightly floured surface, roll out one disc of dough to fit a 9-inch pie pan. Transfer the dough to the pie pan and trim the edges, leaving a 1-inch overhang.
Add Filling. Pour the blueberry filling into the prepared pie crust.
Create Lattice Top. Roll out the second disc of dough and cut into 1-inch wide strips. Arrange the strips over the filling in a lattice pattern. Trim excess dough and crimp the edges to seal.
Apply Egg Wash. In a small bowl, whisk together the egg and milk. Brush the lattice crust with the egg wash.
Bake. Place the pie on a baking sheet to catch any drips. Bake in the preheated oven for 50 minutes, or until the crust is golden brown and the filling is bubbly. If the edges start to brown too quickly, cover them with foil.
Cool. Allow the pie to cool on a wire rack for at least 2 hours before serving to let the filling set. For the neatest slices, refrigerate 2 hours more.
Serve. Slice and enjoy with a scoop of vanilla ice cream or a dollop of whipped cream.