Method
- Make the dough: in a large bowl, whisk 2 1/2 cups flour, 1 tsp sugar, and 1 tsp salt. Add 1 cup cold cubed butter and cut it in with a pastry cutter or your fingers until the mixture looks like coarse crumbs with some pea-sized butter pieces still visible - those butter pieces are what create flaky layers.
- Drizzle in 6 tbsp ice water and mix with a fork, adding up to 2 more tbsp only as needed, until the dough just holds together when pinched. Do not overwork it or add extra water; a shaggy, slightly dry-looking dough is correct.
- Divide the dough into two disks, wrap each in plastic, and refrigerate for at least 1 hour (or up to 2 days). Chilling relaxes the gluten and firms the butter, which is essential for a flaky crust.
- Make the filling: toss the 3 lbs sliced apples with 3/4 cup sugar, 1/4 cup flour, 1 tsp cinnamon, 1/4 tsp nutmeg, and 1 tbsp lemon juice in a large bowl. Let it sit for 15 minutes so the apples release some juice, which the flour will thicken during baking.
- Preheat the oven to 425 F. On a floured surface, roll one dough disk into a 12-inch circle about 1/8 inch thick and fit it into a 9-inch pie dish, letting the excess hang over the edge.
- Pour the apple filling into the crust, mounding it slightly in the center, and dot with any leftover juices from the bowl.
- Roll the second disk into a 12-inch circle and cut it into 8 to 10 strips about 1 inch wide. Lay half the strips across the pie, then weave the remaining strips over and under perpendicular to the first, creating a lattice pattern.
- Trim the overhanging dough to 1 inch, fold the edges under, and crimp decoratively with your fingers or a fork to seal.
- Brush the lattice top with the beaten egg and sprinkle with 1 tbsp coarse sugar for a shiny, crunchy finish.
- Bake at 425 F for 20 minutes, then reduce the oven temperature to 375 F and continue baking for 35 to 40 minutes, until the crust is deep golden brown and the filling is bubbling thickly through the lattice gaps. If the edges brown too fast, cover them loosely with foil.
- Cool the pie on a wire rack for at least 3 hours before slicing; this rest time lets the filling set so it does not run out when cut. Cutting too early is the most common mistake with fruit pies.
Tips
Keep everything as cold as possible - cold butter, ice water, even a chilled bowl - since warm dough is the main reason pie crust turns tough instead of flaky.
Resist cutting the pie warm; a full 3-hour cool-down is what keeps the slices neat instead of a soupy mess.