In a mixing bowl, combine the unbleached all-purpose flour, salt, and sugar.

Add the cold cubed butter to the flour mixture and work it until it resembles coarse crumbs.

Gradually pour in the ice water, mixing gently with a fork until the dough starts to come together.

Turn the dough out onto a lightly floured surface, shape it into a disk, wrap in plastic wrap, and refrigerate for at least 30 minutes.

Prepare the blueberry filling by combining blueberries, sugar, cornstarch, and lemon juice in a medium bowl.

Once the dough has chilled, divide it in half and roll out one portion until it's about 1/8 inch thick.

Use a round cutter to cut out circles from the rolled dough, approximately 4 to 5 inches in diameter.

Place a tablespoon of the blueberry filling in the center of each dough circle, ensuring not to overfill.

Fold each pastry over to create a half-moon and press the edges to seal.

Preheat your oven and create an egg wash by whisking the egg. Brush the tops of each pastry with the egg wash.

Arrange the hand pies on a baking sheet, making sure they don’t touch, and bake until golden brown and firm.

While the pies cool, prepare the icing by mixing powdered sugar and lemon juice until smooth.

Once the pies are completely cool, drizzle or spread the lemon icing over the tops.