Prepare a flaky pie crust recipe that makes 2 (9") pie crusts, one for the base and one for the top. Allow the pie dough to chill for at least 1 hour before rolling out. Alternatively, use a store-bought pie crust according to the package directions.
Position an oven rack in the center of the oven and preheat to 400°F (204°C).
Add the sliced apples, granulated sugar, light brown sugar, flour, cinnamon, nutmeg, lemon juice, and lemon zest to a large bowl. Toss until the apple slices are evenly coated.
Take the pie crust dough out of the refrigerator and leave it at room temperature for 5–10 minutes. Lightly flour your work surface, then roll one disc of dough into a 12" circle that is ⅛" thick. Carefully transfer it to the bottom of a deep-dish pie plate.
Spoon the apple mixture into the bottom crust, leaving behind and discarding the juices collected at the bottom of the bowl. Roll the second disc of pie dough until it is ⅛" thick, then place it over the apple filling.
With a sharp knife, trim the dough around the outside edge of the pie plate. Lift the edges where the upper and lower crusts meet, gently press them together to seal, and fold them underneath. Turn the pie plate as you work until the entire edge is neatly tucked under. Cut 4 slits in the top crust to release steam, then set the pie on a baking sheet.
Brush the top crust with the beaten egg and sprinkle with sanding sugar. Protect the edges with a pie shield or strip of foil so they do not become too brown during the first 25 minutes of baking.
Bake at 400°F (204°C) for 25 minutes. Carefully take off the pie shield and reduce the oven temperature to 375°F. Continue baking for 30–35 minutes, until the top is golden brown and the filling juices are bubbling.
Let the finished pie cool at room temperature for at least 3 hours before serving.