In a saucepan, mix blueberries, granulated sugar, lemon zest and lemon juice and cook it over medium heat for about 10 minutes until the blueberries release all the juices and cook down. When the sauce starts boiling, reduce the heat a bit and let it simmer.
After a total of 10 minutes of cooking, the sauce should be done, reduce the heat to low.
Mix cornstarch with a tablespoon of water and add it to the sauce. Stir well and cook for a couple of minutes until it thickens up.
Remove the sauce from the heat and let it cool off for about an hour.
When ready to bake, preheat the oven to 425°F. Line a cookie sheet with parchment paper and set aside.
Roll out the pie dough and, using a cookie cutter (about 6 inches in diameter), cut out the dough. You can gather all the scraps and re-roll the dough, then cut out more circles. You should have 9 circles total.
Place half of them on a cookie sheet and scoop a tablespoon of blueberry filling on each circle.
In a small bowl, whisk an egg with a tablespoon of water for egg wash. Brush the edges of the circles with the filling. This step will help you to stick the layers so the filling won’t leak.
With a small paring knife, make four small slits in the center of the other half of the circles. Place them on top and slightly press the edges.
Using a fork, press the edges of the hand pies. That will secure them, so they won’t split while baking.
Use the same egg wash and brush the top of the pies. Top them with a little bit of sugar.
Bake at 425°F for about 18-20 minutes, or until the hand pies are beautiful golden/brown color.
Let them cool off before serving.