Instructions:
- Phase 1: The All-Butter Pie Crust. Whisk flour, sugar, and salt in a large bowl. Cut in the cold butter until the mixture resembles coarse crumbs with some pea-sized pieces remaining.
- Gradually sprinkle in the ice water, mixing until the dough just comes together. Divide into two slightly uneven discs (one larger), wrap tightly, and refrigerate for at least 1 hour.
- Phase 2: Preparing the Filling. In a separate bowl, whisk together sugar, cornstarch, cinnamon, and nutmeg.
- Gently fold the blueberries, lemon juice, and zest into the sugar mixture. Set aside.
- Phase 3: Assembly and Baking. On a lightly floured surface, roll out the larger dough disc and carefully fit it into the 9-inch pie dish. Trim the edges, leaving a 1-inch overhang.
- Pour the blueberry filling evenly into the bottom crust. Roll out the second disc and place it over the filling, cutting vents or creating a lattice design.
- Trim the top overhang, tuck it under the bottom edge, and crimp the edges decoratively. Brush the top crust with the egg wash and sprinkle generously with coarse sugar.
- Place the pie on a baking sheet. Bake at 400°F (200°C) for 15 minutes. Reduce the oven temperature to 375°F (190°C) and continue baking for another 45–60 minutes until the filling is bubbling thickly.
- Remove from the oven and allow the pie to cool completely on a wire rack for at least 3 hours before slicing to ensure the filling sets properly.