Preheat the oven. Preheat the oven to 400°F and position a rack in the center of your oven. Line a rimmed baking sheet with parchment paper.
Make the blueberry filling. In a large bowl, stir together the blueberries, sugar, lemon zest, lemon juice, corn starch and salt. Set aside while you roll out the pie dough. 4 cups blueberries ⅓ cup (67 g) granulated white sugar 1 teaspoon lemon zest 1 tablespoon lemon juice 2 tablespoons cornstarch Pinch salt
Roll out the chilled pie dough: On a floured work surface,with a rolling pin, roll out the disc of pie dough. Turn the dough a quarter turn after every few rolls until you have a circle 12-inches in diameter. 1 pie crust
Form the crostata. Place the dough onto a parchment paper rimmed lined baking sheet. Add the fruit mixture to the center of the dough, leaving a 2” border. Fold the border over the filling, leaving the center exposed, overlapping where necessary. Chill in the fridge for 15-30 minutes to help with chilling pie crust and preventing leaks.
Make an egg wash. In a small bowl, whisk together the egg and 1 tablespoon of water. Brush the crust edges with the egg wash, and sprinkle with coarse sugar. You won’t use the whole egg wash. Egg wash: 1 beaten egg + 1 tablespoon of water Coarse sugar
Bake the crostata. Bake the crostata for about 40- 45 minutes until golden brown and the filling is bubbling. Transfer the galette to a wire cooling rack to cool at least 20 minutes. Serve warm or room temperature.