Preheat the oven to 375°F and line a baking sheet with foil.
Add the sliced apples to a large bowl and toss with lemon juice to prevent browning. Stir in the granulated sugar, brown sugar, flour, cinnamon, and nutmeg. Mix until evenly coated.
3 pounds apples, 1 tablespoon freshly squeezed lemon juice, ⅓ cup granulated sugar, ⅓ cup light brown sugar, ¼ cup all-purpose flour, 1 ½ teaspoons ground cinnamon, ¼ teaspoon ground nutmeg
Let the mixture sit for 1–4 hours at room temperature to allow the apples to release excess liquid.
After resting, use a slotted spoon to transfer the apples to a pan. Cook over low-medium heat for 8–10 minutes, stirring occasionally, until they begin to soften.
Pour the reserved liquid into a small saucepan or the same skillet after removing the apples. Simmer the liquid over medium heat until it reduces to about ½ cup and thickens into a syrup.
Stir the syrup back into the cooked apples and let the filling cool slightly while preparing the crust.
Place the bottom crust into a 9-inch pie pan, pressing it gently into place. Use a fork to poke holes in the bottom and sides of the crust. Optional: apply a light layer of egg wash to the bottom and sides of the crust to form a barrier against excess moisture.
Spoon the cooled apple filling into the crust and dot the top with the cubed butter.
3 tablespoons unsalted butter
Roll out the top crust and place it over the filling. Trim any excess dough, then crimp the edges to seal. Cut 4–5 vents in the top to allow steam to escape, or make a lattice top if desired.
Whisk the egg and water together, then brush evenly over the top crust.
1 large egg, 1 tablespoon water
Place the pie on the prepared baking sheet and bake for 55–65 minutes, or until the crust is golden brown and the filling is bubbling through the vents.
Let the pie cool completely for at least 2–3 hours before slicing. This allows the filling to fully set and prevents it from running.