Preheat the oven to 400°F. Place a sheet tray on the lower rack in the oven. Gently place one of the pie crusts into a 9-inch x 2-inch deep pie plate with the crust overlapping the sides. Place into the refrigerator with the other crust until ready to assemble.
In a large bowl, add the blueberries, sugar, cornstarch, lemon juice, cinnamon, and sea salt.
Mix until everything is coated, set aside.
Roll out the second crust onto a clean work surface. Cut the crust into 1-inch strips. I like to use a ruler to help make straight lines. Set aside.
Take the pie plate out of the fridge and fill it with the blueberry filling. Dot with the butter if using.
Take 5 of the pie crust strips and lay them out parallel to each other with a small gap on top of the pie. You want to use the longer strips in the center of the pie and the shorter ones towards the edge.
Take every other strip and fold it up over itself so the filling is exposed under those pieces. Lay 1 strip of pie crust on top. Fold the strips back over so you now have part of a weave.
Do this process again but with the remaining strips. Repeat until the entire pie has lattice.
Tuck the edges of the strips under the edge of the bottom pie crust. Crimp the edges around the entire pie.
In a small bowl, whisk the egg with the milk.
Brush this mixture over the exposed pie crust.
Sprinkle the sugar on top of the crust.
Bake for 20 minutes at 400*F. At the 20 minute mark, add a foil tent over the pie and lower the heat to 350°F. Continue to bake for 35-45 minutes until the crust is golden brown and the filling is bubbly.
Let sit out at room temperature for 3-4 hours until the filling has set. Serve as-is or with your favorite toppings.
You can use your own homemade pie crust recipe if you like.
Frozen blueberries can be used, but make sure to defrost and drain them first.
This needs to sit for about 3-4 hours to have time for the filling to set up.