I combine the flour, salt, and sugar in a large bowl, then cut in the cold cubed butter using a pastry cutter until it looks like coarse crumbs. I add ice water one tablespoon at a time, mixing gently just until the dough comes together. Overworking it here is the biggest mistake I used to make, so I stop as soon as it holds.
I divide the dough into two discs, wrap them in plastic wrap, and refrigerate for at least an hour. This resting time relaxes the gluten and keeps the butter firm, which is exactly what gives this apple pie crust recipe its flaky layers. Don't skip this step, even if you're in a hurry.
While the dough chills, I peel, core, and thinly slice my apples, then toss them with lemon juice right away. In a separate bowl, I whisk together the sugars, flour, cinnamon, and nutmeg before pouring it over the apples. I mix everything gently until every slice is coated evenly.
I lightly flour my work surface and roll one dough disc into a circle about two inches wider than my pie dish. I carefully transfer it into the dish, pressing it gently into the corners without stretching it. Stretched dough tends to shrink back during baking, so I take my time here.
I pour the apple filling into the crust, mounding it slightly in the center, and dot it with the cubed butter. Then I roll out the second disc and either lay it whole over the top with slits cut in or weave it into a lattice. I trim the excess dough and crimp the edges to seal everything in.
I brush the top crust with the beaten egg and sprinkle on the coarse sugar for a beautiful golden finish. I bake it at 425°F for 20 minutes, then lower the oven to 375°F and bake for another 35 to 40 minutes. I cover the edges with foil halfway through so they don't burn before the center is done.
I always let my pie cool on a wire rack for at least two hours before slicing it. I know it's tempting to cut in right away, but the filling needs that time to set, or it will run all over the plate. Patience here really does pay off.