Make the dough. In a bowl, whisk 2 1/2 cups flour and 1/2 teaspoon salt. Cut in 1 cup cold unsalted butter (cubed) until the mixture looks like coarse crumbs with pea-size bits. Drizzle in 6–8 tablespoons ice water, mixing just until the dough holds together when pressed. Divide into two disks, wrap, and chill for 30 minutes.

Prep the filling. In a medium bowl, toss 2 cups blueberries with 1/3–1/2 cup sugar (adjust to sweetness), 1 1/2 tablespoons cornstarch, 1 teaspoon lemon zest, 1 tablespoon lemon juice, a pinch of salt, and a pinch of cinnamon if using. Set aside for 10 minutes to let the berries release a little juice.

Heat the oven. Preheat to 400°F (200°C). Line two baking sheets with parchment paper.

Roll out the dough. On a lightly floured surface, roll one dough disk to about 1/8 inch thick. Cut into 4–5 inch circles or rectangles. Gather scraps, re-roll, and cut more shapes. Repeat with the second disk. Aim for 10–12 pieces total to make 5–6 pies.

Fill and seal. Spoon 1–2 tablespoons of blueberry filling onto the center of half the dough pieces, leaving a border. Lightly brush edges with water. Top with the remaining dough pieces. Press edges to seal, then crimp with a fork.

Vent and finish. Cut small slits on top of each pie to vent steam. Beat 1 egg with 1 tablespoon water for an egg wash. Brush the tops and sprinkle with coarse sugar for crunch.

Chill briefly. Transfer the assembled pies to the fridge for 10 minutes. This helps them keep their shape and bake up flaky.

Bake. Bake for 18–22 minutes, until golden brown and bubbling at the vents. Rotate pans halfway through for even browning.

Cool. Let the pies cool on the baking sheet for 5 minutes, then move to a rack. Serve warm or at room temperature.

Optional glaze. For extra shine, whisk 1/2 cup powdered sugar with 1–2 teaspoons lemon juice and drizzle over cooled pies.