Make the filling: In the same large bowl with the apples, add the granulated sugar, all-purpose flour, ground cinnamon, ground nutmeg, and salt. Mix gently until the apples are evenly coated with the dry ingredients. Set aside.

Preheat oven and prepare baking sheet: Preheat your oven to 400°F (200°C). Line a large baking sheet (e.g., 13×18 inch) with parchment paper.

Roll out the first crust: On a lightly floured surface, roll out one portion of the pie crust dough into a rectangle about 1/8-inch thick. Carefully transfer it to the prepared baking sheet.

Add the filling: Spread the prepared apple mixture evenly over the bottom crust on the baking sheet, leaving a 1–2 inch border around the edges.

Create a rustic edge: Fold the exposed edges of the bottom crust inward over the apple filling to create a simple, rustic frame.

Roll out the second crust: Roll out the second portion of the pie crust dough into another rectangle slightly larger than the first one.

Top with the second crust: Carefully place the second rolled-out crust directly over the apple filling.

Seal and vent: Use a fork or knife to crimp and seal the edges of the top and bottom crusts together. Cut several slits in the top crust to allow steam to escape during baking.

Prepare egg wash: In a small bowl, beat the egg yolk with 1 tablespoon of water to create an egg wash.

Brush and sprinkle: Brush the top crust generously with the prepared egg wash for a golden sheen. If desired, sprinkle the top with coarse sugar or turbinado sugar for extra crunch and sparkle.

Bake: Place the baking sheet in the preheated oven and bake for 25–30 minutes, or until the crust is golden brown and the filling is bubbly. If the crust starts to brown too quickly, you can loosely cover the edges with aluminum foil.

Cool: Remove the apple slab pie from the oven and let it cool on the baking sheet for at least 30 minutes to allow the filling to set slightly before slicing.

Slice and serve: Slice the slab pie into squares or rectangles and serve warm, at room temperature, or chilled. It’s delicious on its own or paired with vanilla ice cream, whipped cream, or a drizzle of caramel sauce.