Instructions:
Prepare the Dough:
In a large bowl, mix together the flour, sugar, and salt. Add the cold butter pieces and toss to coat them with flour.
Using your hands, a pastry blender, or two knives, break the butter into small pieces, slightly larger than peas.
Gradually add 1/2 cup of cold water and stir with a rubber spatula until the dough begins to come together. If it’s still dry, add a little more water, one tablespoon at a time, until the dough forms a soft, slightly loose ball.
Divide the dough into two portions—one slightly larger than the other. The larger portion will be for the bottom crust. Shape each portion into a 1-inch thick rectangle. Wrap each piece in plastic wrap and refrigerate for at least 2 hours.
Prepare the Filling:
In a large bowl, toss the apple pieces with lemon juice.
In a medium bowl, combine the sugar, cornstarch, cinnamon, nutmeg, allspice, and salt. Sprinkle this mixture over the apples and stir to coat them evenly. Set aside.
Assemble the Slab Pie:
Preheat the oven to 375°F (190°C). Line a 10×15-inch baking sheet with parchment paper.
On a floured surface, roll out the larger dough portion into an 18×13-inch rectangle. Transfer the dough to the prepared pan, gently pressing it into the corners. Let the edges of the dough overhang the sides of the pan slightly. Place the pan in the fridge while rolling out the second piece of dough.
Roll the second piece of dough into a 16×11-inch rectangle. Keep it in the fridge while preparing the pie.
Pour the apple filling (and any juices) onto the bottom crust in the pan. Don’t worry if the apples seem piled high—they will shrink as they bake.
Lay the second piece of dough over the apples. Trim both dough layers so they overhang the pan by about 3/4 inch. Crimp the edges to seal.
Brush the top crust with heavy cream or egg wash. Use a sharp knife to make several 1-inch slits in the crust to allow steam to escape during baking.
Place the pie pan on a larger baking sheet to catch any spills. Bake for 40-45 minutes, until the crust is golden brown and the filling is bubbling through the slits.
Let the pie cool on a wire rack for at least 45 minutes before cutting and serving.
