Combine All-Purpose Flour (2 1/2 cup), Salt (1 teaspoon), and Granulated Sugar (2 tablespoon). Whisk to combine.
Add the Unsalted Butter (1 cup) and begin to work butter into flour mixture using your fingertips or a pastry blender.
Break down butter until it resembles coarse meal and the largest bits are the size of small peas. The butter should still be cold once you have reached the coarse meal stage. Rechill the mixture for about 10 minutes in the freezer. If it becomes too soft while doing this, stick everything in freezer for 10 to 15 minutes and then begin again. You can do this multiple times without any harm.
Using a fork, stir in Buttermilk (1/2 cup) and mix until dough ball starts to form - have a tablespoon or 3 extra of buttermilk at the ready if dough is dry.
Empty contents out onto a lightly floured surface and divide into two even pieces. Knead dough just a few times to form a shaggy ball of dough.
Flatten into two disks and wrap in plastic wrap and place in refrigerator for at least one hour and up to 48 hours.
Preheat oven to 425 degrees F (220 degrees C).
Remove one disk of dough from fridge and on a lightly floured surface, roll out dough until it is about 1/8 inch thick and 12 inches in diameter.
Fit dough into a 9 inch pie plate, trim off excess dough around edges - leaving about 1/2 inch overhanging the edge. Place pie plate in freezer for 15 minutes. Prepare filling.
In a large bowl, combine Fresh Blueberries (4 cup), Granulated Sugar (2/3 cup), Instant Tapioca (3 tablespoon), Salt (1 pinch), Ground Cinnamon (1/4 teaspoon), and zest of a Lemon (1) and juice from half of that lemon. Toss to combine.
Remove second disk of dough from fridge and roll out dough into a circle about 12 inches in diameter and 1/8-inch thickness (thereabouts). With a knife or a pizza slicer, cut into 1 inch wide strips.
Remove pie crust from freezer and pour blueberry filling into pie crust. Dot filling with pieces of Unsalted Butter (1 tablespoon).
Taking strips of pie crust, lay them across the pie, either using a lattice pattern or any which way. Crimp the edges of the pie crust, folding under excess pie crust along the edges.
Beat an Egg (1), Water (1 teaspoon) and a little Salt (1 pinch) together to make an egg wash. Brush top of the crust with egg wash and sprinkle with Raw Sugar (to taste).
Place pie on a rimmed baking sheet and place on middle rack in preheated oven and let bake for 20-25 minutes until the top and edges begin to brown.
Reduce oven temperature to 350 degrees F (180 degrees C) and continue to bake for an additional 30 to 40 minutes until the pie is golden brown and the filling is bubbling throughout.
Remove from oven and place on cooling rack and let cool completely before enjoying.