Preheat your oven to 220°C and place the rack in the lower third.

Mix the filling by gently folding fresh blueberries, granulated sugar, cornstarch, ground cinnamon, kosher salt, and fresh lemon juice in a large mixing bowl.

Flour a clean work surface lightly and unroll two pie crusts, stacking one on top of the other.

Transfer the rolled dough to a quarter sheet pan, pressing it into the corners with excess dough hanging over the sides.

Brush the base of the crust with beaten egg white to prevent sogginess.

Pour the prepared blueberry filling over the crust and spread it evenly.

Roll out the third pie crust into a 30-centimeter circle and cut it into 14 strips for the lattice topping.

Weave your strips diagonally over the pie, creating a lattice design.

Trim the edges of the pastry and roll towards the center to create a neat border.

Brush the lattice crust with the beaten egg and sprinkle with coarse sanding sugar if desired.

Bake the pie for 30 minutes, then shield with foil and bake for another 20 minutes, until golden brown.

Cool the pie at room temperature for at least one hour before slicing.