In a large mixing bowl, whisk together 3¾ cups of all-purpose flour, 1½ tablespoons of sugar, and 1½ teaspoons of salt. Cut in 3 sticks of very cold unsalted butter until the mixture resembles coarse crumbs. Gradually stir in ¾ cup of very cold water until the dough begins to form. Divide the dough into two rectangles, wrap them in plastic wrap, and chill in the refrigerator for at least 2 hours.

In a sizable bowl, toss 10 cups of peeled, cored, and chopped apples with a squeeze of fresh lemon juice to prevent browning. Add ¾ to ¾ cup sugar, 3 tablespoons of cornstarch, 1 rounded teaspoon of ground cinnamon, ¼ teaspoon of ground nutmeg, ¼ teaspoon of ground allspice, and ⅛ teaspoon of salt. Stir until combined and allow the mixture to sit, letting the flavors meld and the juices blend.

While the filling sits, preheat your oven to 375°F (190°C). Line a jelly roll pan (18x13 inches) with parchment paper, ensuring the paper overhangs a bit for easier removal later.

On a floured surface, take the larger piece of chilled dough and roll it out to fit the dimensions of the jelly roll pan. Aim for an even thickness of about ⅛ inch. Carefully transfer the rolled dough into the prepared pan, pressing it gently to fit the corners.

Pour the prepared apple filling into the crust-lined pan, making sure it’s evenly spread. Carefully place the second rolled-out dough over the filling and crimp the edges to seal. Make several slits in the top crust for steam to escape, then brush the surface with 2 tablespoons of heavy cream or an egg wash.

Once assembled, place the Apple Slab Pie in the preheated oven and bake for 40-45 minutes until golden brown and bubbly.

After baking, remove the pie from the oven and let it cool on a wire rack for at least 45 minutes.