To make the dough, whisk the flour and salt together in a large bowl. Add the butter and shortening. Using two forks, cut the butter and shortening into the mixture to break up the cold butter mixture into tiny little flour-coated pieces; you’re not completely incorporating it. Do not overwork the ingredients.
Measure 1/2 cup of water in a cup. Add ice. Stir it around. Measure 1/2 cup of that ice water. Drizzle the cold water in, 1 Tablespoon at a time, and stir with a rubber spatula or wooden spoon after every Tablespoon has been added. Stop adding water when the dough begins to form large clumps. Do not add any more water than you need.
Transfer your dough to a floured work surface. Using floured hands, fold the dough into itself until the flour is fully incorporated into the butter mixture. The dough should come together easily and should not feel overly sticky. Avoid overworking the dough. If it feels a bit too dry or crumbly, dip your fingers in the ice water and then continue bringing dough together with your hands. If it feels too sticky, sprinkle on more flour and then continue bringing dough together with your hands. Form it into a ball. Use a sharp knife to cut it in half. If it’s helpful, you should have about 1 lb, 8 ounces dough total. Gently flatten each half into 1-inch-thick discs using your hands. Wrap each tightly in plastic wrap. Refrigerate for at least 2 hours and up to 5 days.
Make your filling: In a large bowl, stir the apple slices, sugars, flour, lemon juice, cinnamon, allspice, and nutmeg together until thoroughly combined. Preheat oven to 400°F.
Roll out the chilled pie dough. On a floured work surface, roll out one of the discs of chilled dough (keep the other one in the refrigerator). Turn the dough about a quarter turn after every few rolls until you have a circle 12 inches in diameter. Carefully place the dough into a 9-inch pie dish that’s 1.5 to 2 inches deep. Tuck the dough in with your fingers, making sure it is smooth. Spoon the filling into the crust. It’s ok if it is still warm from the precooking step. It will seem like a lot of apples; that’s ok. Pile them high, and tightly together
Remove the other disc of chilled pie dough from the refrigerator. Roll the dough into a circle that is 12 inches diameter. Using a pastry wheel, sharp knife, or pizza cutter, cut strips of dough; in the pictured pie, I cut 12 1-inch-wide strips. Carefully thread the strips over and under one another, pulling back strips as necessary to weave. Trim off excess dough. Fold the overhang back towards the center of the pie, and pinch the edges to adhere the top and bottom crusts together. Crimp the edges of the crust to seal.
Lightly brush the top of the pie crust with the egg wash. Sprinkle the top with coarse sugar, if using. Place the pie onto a large baking sheet and bake for 25 minutes. Then, keeping the pie in the oven, reduce the oven temperature down to 375°F (190°C). Continue baking the pie until the filling is bubbling around the edges, 35–40 more minutes. This sounds like a long time, but under-baking the pie means an unfinished filling with firm apples with paste-like flour.
Remove pie from the oven, place on a cooling rack, and cool for at least 3 hours before slicing and serving. Pour yourself a glass of Chardonnay and enjoy!