First, make the pie crust: In the bowl of a food processor, pulse flour, 1 teaspoon granulated sugar, and salt until well-combined. Add cold butter cubes and shortening; pulse mixture repeatedly until butter and shortening are incorporated and butter is the size of small peas. Gradually pour in 4 tablespoons ice water, pulsing mixture repeatedly, just until a dough comes together (if the dough seems dry, add in 1 to 2 tablespoons more ice water).
Transfer dough to a sheet of plastic wrap. Gently pat into a disc shape, about 1 inch thick, and cover tightly with plastic wrap. Refrigerate for at least 2 hours, or up to 3 days, before using.
Next, make the blueberry filling: In a medium bowl, toss blueberries with 1/4 cup granulated sugar, cornstarch and lemon juice.
Finally, assemble and bake: Preheat your oven to 375°F. On a lightly floured surface, roll out chilled pie dough to a rough 12-inch circle; transfer to a parchment paper-lined rimmed baking sheet. Mound blueberry filling in the middle of the crust, leaving at least a 2-inch border along the edges. Fold the pie crust edges over, overlapping slightly. Brush dough with milk and 1 tablespoon sparkling sugar, if desired.
Bake for 40 to 45 minutes or until filling is bubbly and pie crust is golden-brown and baked through. Cool at least 15 minutes on baking sheet before serving.