In a large bowl, put the flour, and cubed butter for the crust. Use your hands to smush the butter into the flour. Incorporate some and leave some small flakes visible. Then add 2 tbsp of water and start to gather the flour into a ball of dough. If you need more water, add it 1 tbsp at a time. Once it's gathered into a ball, separate into two discs and wrap them in siran wrap. Refrigerate for 20 minutes.
In another large bowl, mix blueberries, butter, cinnamon, nutmeg, lemon zest, vanilla, sugar, salt, and cornstarch.
Preheat oven to 350°F. Roll out one disc of crust dough on a lightly floured surface. Try and roll it out into a circle that's about ⅛" thick. Then cut out a 9-10" circle. Keep the remainder dough and chuck it. Put the circle on a baking sheet with parchment paper.
Then put filling into the middle of the circle leaving a 2" border. Fold the crust over the filling. Brush the crust with an egg white, then sprinkle sugar onto the crust.
Bake for 20-30 minutes until the crust is golden brown. Let cool a few minutes before attempting to move onto a plate. Enjoy!
**Vegan Option: Brush a tbsp of melted dairy free butter onto the crust as an "egg wash" instead.