In a food processor add the flour, salt, and sugar. Cube the cold butter into little cubes and add to the flour. Place the lid onto the food processor and pulse until the butter is the size of peas.
Fill a glass with water and add ice, then measure out ⅓ cup of cold water.
Slowly add to the food process a tablespoon at a time, pulsing in between each addition. Once it’s all been added, pulse until the dough comes together. If it’s still dry, pulse a little longer until the dough forms. Divide the dough in half.
Place a piece of plastic wrap onto a clean surface and place half the dough onto the wrap. As you wrap the dough, form it into a disc. Repeat with the other half of the dough. Place in the refrigerator for at least 1 hour.
Right before you pull the dough out of the refrigerator, prepare the blueberries. In a medium bowl toss the blueberries with sugar, corn starch, and lemon juice. Set aside.
Make an egg wash by beating one egg in a small bowl, set aside.
Remove one disc of dough from the refrigerator. Sprinkle a few tablespoons of flour onto a clean surface. Roll out the dough until it’s ¼ inch thick. Using a 4-inch cookie cutter, cut out circles, place them on a baking sheet lined with parchment paper. Roll the leftover dough back out and cut out more pieces.
Brush the edges of each circle with egg wash. Place 1 to 2 tablespoons of blueberries in the middle of one piece of dough. Place the second piece on top. Use a fork to seal the edges. Brush the tops with egg wash.
Bake at 400°F for 15 to 20 minutes until golden brown. Remove from oven and transfer to a cooling rack.
To make the glaze, whisk the powdered sugar and lemon juice together. Drizzle over the top of each pie. Let cool before serving.