Preheat oven to 375 degrees (F), and place a rack to the bottom position in the oven.
Roll dough into a 10-inch circle and transfer to a parchment-lined baking sheet.
Using the tines of a fork, dock the dough in the center a few times.
Place blueberry filling onto the center of the dough. Fold the edges of the dough up around the blueberry filling, leaving the filling in the center exposed.
Whisk the reserved egg white and lightly brush the dough with it. If desired, sprinkle the dough with ½ tablespoon of sugar.
Bake until the filling is bubbly and crust is golden brown, 30 to 35 minutes.
Allow to cool slightly, about 30 minutes, before serving!