1. Make the Pie Dough:

• In a large bowl, combine the flour, sugar, and salt.
• Add the cold, cubed butter and use a pastry cutter, fork, or your hands to work the butter into the flour until the mixture resembles coarse crumbs with pea-sized pieces of butter.
• Slowly add the ice water, 1 tablespoon at a time, and mix until the dough just comes together. Be careful not to overwork it. If the dough is too crumbly, add more ice water, 1 tablespoon at a time.
• Divide the dough into two equal portions, form each into a disc, and wrap tightly in plastic wrap. Refrigerate for at least 1 hour to chill and firm up.

2. Prepare the Filling:

• In a medium bowl, combine the blueberries, sugar, cornstarch, lemon juice, lemon zest, vanilla extract, and salt. Gently stir to combine, making sure the blueberries are coated evenly.
• Set aside to let the mixture sit for 10-15 minutes while you roll out the dough.

3. Roll Out the Dough:

• Preheat the oven to 375°F (190°C) and line a baking sheet with parchment paper.
• On a lightly floured surface, roll out one disc of dough to about 1/8-inch thickness. Using a round cutter (about 4-5 inches in diameter), cut out circles of dough. You should get about 6-8 circles, depending on the size.
• Place a heaping tablespoon of the blueberry filling in the center of each dough circle, leaving a small border around the edges.

4. Assemble the Hand Pies:

• Lightly wet the edges of each dough circle with a bit of water and fold the dough over the filling to create a half-moon shape.
• Press the edges together with a fork to seal the pies securely.
• In a small bowl, whisk together the egg and 1 tablespoon of water to make an egg wash. Brush the tops of the hand pies with the egg wash and sprinkle with a little granulated sugar.

5. Bake the Pies:

• Place the hand pies on the prepared baking sheet and bake for 20-25 minutes, or until the crust is golden brown and the filling is bubbling through the edges.
• If the edges start to brown too quickly, cover the pies with foil and continue baking until done.

6. Cool and Serve:

• Let the hand pies cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.
• Serve as a sweet snack, dessert, or treat for any occasion!