Preheat oven to 375°F.
Place the pie dough on a parchment-lined baking sheet. Combine the granulated sugar with lemon zest. Rub together until the sugar seems damp. Add the cornstarch and stir to combine. Gently stir in the blueberries.
Place the blueberries onto the pie dough, leaving about a one-inch border around the edge.
If desired, sprinkle sugar over the edges of the dough.
Bake until the filling bubbles and the crust is golden brown, about 40 minutes. Allow the galette to cool for about 15 minutes before serving.
Store the galette in the refrigerator for up to three days.