Preheat oven to 375°.
In a small bowl, mix together sugar, cornstarch, and cinnamon. In a large bowl, gently mix blueberries with lemon juice to coat. Sprinkle sugar mixture over blueberries and gently mix until blueberries are completely coated.
Combine egg yolk and water to create egg wash.
Using a small 4-to-5 inch bowl as a template and a sharp knife, cut 3 or 4 circles out of each prepared pie crust. Leftover pieces can be used to form complete circles if necessary. Place dough circles on a parchment paper-lined baking sheet.
Fill the center of pie crusts with 1-2 tablespoons of blueberry mixture. Brush edges with egg wash. Fold crust in half and seal edges by pressing the back of a fork down on top edge of dough.
Chill hand pies for 30 minutes in the refrigerator before baking. Remove from refrigerator and brush top sides with remaining egg wash. Sprinkle tops with sanding sugar. Cut a small slit in the tops of the hand pies to let steam escape during baking.
Bake 20 minutes or until pies have turned golden brown and are flaky.
Let pies cool for 5 minutes before serving.
Enjoy!