Preheat your oven to 425°F (220°C).
Prepare a 9-inch pie pan. Lightly grease with butter or nonstick spray.
To make the filling: In a large bowl, combine the apple slices, granulated sugar, tapioca flour, cinnamon, salt, nutmeg, and mix until thoroughly combined.
10 cups (1250g), Honeycrisp apple slices, about 8 large apples, peeled and cored, cut 1/4 inch thick, 3/4 cup (150g) Granulated sugar, 1 1/2 teaspoons Cinnamon, 1/4 teaspoon Ground nutmeg, 1/2 teaspoon (2 grams) Diamond Crystal kosher salt;, 1/4 cup Tapioca flour (30g) or cornstarch
In a small bowl, Combine the granulated sugar, flour, and cinnamon. Set aside.
To assemble the pie: On a floured surface, roll out one disc of chilled pie dough until it forms a 12" circle. Place it into a 9-inch pie dish.
Spread the sugar, flour, and cinnamon on the bottom of the crust.
1 teaspoon Granulated sugar, 1 teaspoon Tapioca flour, cornstarch or all-purpose flour, 1/2 teaspoon Cinnamon
Spoon the prepared apple filling into the pie crust, piling it high and tightly.
Roll the second dough disc into a 12-inch circle. Place over apples. Trim excess, fold edges under, and crimp to seal.
Brush with egg wash and sprinkle with coarse sugar.
1 large egg plus 1 tablespoon water,
Cut at least 4 slits in the top.
Place pie on a parchment-lined baking sheet. Bake at 425°F (220°C) for 15 minutes, then reduce to 375°F (190°C) and bake 40–45 minutes, until golden and bubbling.
Cool at least 4 hours (or overnight) before slicing to allow the filling to set.
Store any leftover pie, lightly covered, at room temperature for several days. Freeze for longer storage.