Line cookie sheets with parchment paper and set them aside.
Place the berries in a medium-sized bowl
In a small box mix together lemon zest, lemon juice, and cornstarch.
Pour lemon juice mixture over the berries. Gently stir with a large spoon to combine the berries and dry ingredients until no white bits remain.
Taste the berries and if you want them sweeter add sugar 1 tablespoon at a time until the desired sweetness is reached. Refrigerate the berries while you roll out the pie dough.
The size of them can be left up to you. I made mine about 9" round, and then when I was getting to the end of the dough they became smaller.
Spoon 1/4 cup of the blueberry mixture into the center of the galette dough. Leave one inch at the border to fold over the top of the blueberries.
Fold over dough and pinch. Then brush egg wash (1 egg and 1 tbsp of water) and you can sprinkle with sugar if you'd like. I didn't but the option is there.
Bake in a 350-degree oven for 15 minutes, or until the crust is golden brown.
