Cook blueberries, ½ cup sugar, lemon zest, salt, and cinnamon in medium saucepan over medium heat, stirring occasionally, until blueberries begin to break down and release their juices, about 8 minutes. Reduce heat to medium-low and continue to cook until mixture thickens and spatula starts to leave trail when pulled through, 8 to 10 minutes.

Whisk cornstarch and water together in bowl, then stir into blueberry mixture. Cook until mixture has thickened to jam-like consistency, about 1 minute (you should have about 1¼ cups filling). Let cool completely, about 30 minutes.

Adjust oven rack middle position and heat oven to 400 degrees. Line rimmed baking sheet with parchment paper. Working with 1 sheet of pastry at a time, roll into 10-inch square on floured counter. Cut pastry into four 5-inch squares. Place 2 tablespoons blueberry filling in center of each square.

Brush edges of squares with egg wash, then fold dough over filling to form rectangle. Using fork, crimp edges of dough to seal. Transfer pies to prepared sheet and cut three 1-inch slits on top (do not cut through filling). Freeze pies until firm, about 15 minutes. (Once frozen, pies can be transferred to airtight container and stored in freezer for up to 1 month.)

Brush tops of pies with remaining egg wash and sprinkle with remaining 1 tablespoon sugar. Bake until well browned, about 25 minutes, rotating sheet halfway through baking. Transfer pies to wire rack and let cool slightly, about 15 minutes. Serve warm or at room temperature.