Step 1: Make the Pie Crust

1. In a large bowl, whisk together 5 cups flour, 1/4 cup sugar, and 1/2 teaspoon salt.
2. Cut 2 cups very cold butter into small cubes and add to the flour mixture. Toss with a spatula to coat the butter.
3. Using a pastry cutter, work the butter into the flour until the mixture resembles coarse meal with pea-sized butter pieces.
4. Gradually add 3/4 cup ice water, mixing with a silicone spatula until the dough begins to form moist clumps. Add more water only if absolutely necessary.
5. Turn the shaggy dough onto a clean surface and gently knead just until it comes together.
6. Divide the dough in half (each half should weigh about 644g), shape into disks, wrap in plastic wrap, and refrigerate for at least 2 hours or up to 24 hours.

Step 2: Prepare the Blueberry Filling

1. In a medium saucepan, combine half the blueberries (1 pound/397g), 1/3 cup brown sugar, 2 tablespoons lemon juice, and 1 tablespoon cornstarch.
2. Cook over medium-high heat, stirring constantly, until the mixture simmers and begins to thicken (about 7-8 minutes).
3. Reduce heat to low and cook for 2 more minutes, then remove from heat.
4. Transfer to a large heatproof bowl and add the remaining blueberries, 2/3 cup granulated sugar, 1/2 teaspoon cinnamon, 1/4 teaspoon each of allspice and salt, 1 1/2 tablespoons vanilla extract, 2 tablespoons butter, and the remaining 3 tablespoons cornstarch.
5. Mix thoroughly and set aside to cool completely.

Step 3: Prepare the Bottom Crust

1. Remove one disk of dough from the refrigerator 15 minutes before rolling.
2. On a lightly floured surface, roll the dough from the center outward, rotating a quarter turn after each stroke, until you have a circle about 16 inches in diameter and 1/4 inch thick.
3. Carefully fold the dough in half and place it in a 9-inch pie pan, with the fold in the center.
4. Unfold and gently press the dough into the pan, ensuring there are no air pockets.
5. Trim the overhang to 1 1/2 inches beyond the rim, then refrigerate for at least 20 minutes.

Step 4: Prepare the Lattice Top

1. Remove the second disk of dough from the refrigerator 15 minutes before rolling.
2. Roll out as before to a 16-inch diameter circle.
3. Using a pizza cutter or pastry wheel, cut the dough into 12 strips, each just over 1 inch wide.
4. Place the strips on a parchment-lined baking sheet, cover with plastic wrap, and refrigerate for at least 20 minutes.

Step 5: Assemble and Bake

1. Preheat your oven to 425°F (220°C).
2. Sprinkle 1 teaspoon of flour on the bottom of the chilled pie crust, then add the cooled blueberry filling.
3. Create a lattice pattern with the dough strips: lay 7 strips parallel across the pie, leaving 1/4-inch between them. Fold back alternating strips and weave perpendicular strips through to create the lattice pattern.
4. Trim the lattice strips to 1/2 inch overhang, then roll and crimp the edges to seal.
5. Whisk together 1 egg and 1 1/2 teaspoons water, then brush this egg wash over the lattice and crust edges.
6. Sprinkle with 1/4 cup sparkling sugar.
7. Place the pie on a baking sheet and bake in the lower third of the oven for 15 minutes.
8. Reduce temperature to 350°F (175°C) and bake for an additional 55 minutes, until the crust is golden and the filling is bubbling.
9. Cool on a wire rack for at least 4 hours before slicing.