Preheat the oven to 375°F (190°C) with a pizza stone positioned on the center rack. The stone helps distribute heat to the bottom of the pie dish for a crisp, evenly baked crust.
Remove the prepared pie crust from the refrigerator. Transfer the apples to the crust, pressing them down gently to eliminate large gaps. Mound the apples slightly above the rim of the pie dish, as they will shrink during baking.
Scatter the diced butter evenly over the apples.
1 ounce cold unsalted butter
Arrange five or six pastry strips vertically across the apple filling, spacing them evenly apart. Fold every other strip back toward the center of the pie.
Lay one unused pastry strip horizontally across the center of the pie, over the unfolded vertical strips. Return the folded strips to their original positions over the horizontal strip.
Fold back the alternate vertical strips toward the center. Place another horizontal strip next to the first, leaving a small gap. Unfold the vertical strips over the new horizontal strip.
Repeat the alternating folding and weaving process until one half of the pie is covered. Continue with the other half until the lattice is complete.
Trim the lattice strips to match the edge of the pie dish. Fold the bottom crust over the ends of the lattice strips and crimp or flute the edges to seal. Add decorative pastry leaves or braids if desired.
In a small bowl, whisk the egg with one tablespoon (15 milliliters) of water. Brush the lattice and edges of the crust with the egg wash, then sprinkle lightly with demerara or granulated sugar.
1 large egg, 1 tablespoon water, pinch of demerara or granulated sugar
Place the pie directly on the preheated pizza stone and bake for 30 minutes. Rotate the pie and continue baking for another 30 minutes, or until the crust is golden brown and the filling is bubbling. If the crust browns too quickly, loosely cover it with aluminum foil.
Insert an instant-read thermometer into the center of the filling. The internal temperature should reach 195°F (90°C).
Remove the pie from the oven and allow it to cool in the dish on a wire rack for at least one hour before slicing.