Step 1

To make the crust: Measure the flour into a large, wide bowl. Whisk in the sugar and salt. Toss in the butter cubes and coat them all with the flour. Using your first 3 fingers of both hands, mash up the butter into smaller pieces, just bigger than the size of peas. You can also do this with two knives or a strong pastry blender. I prefer using my fingers.

Step 2

Once the mixture looks sort of uniform, slightly crumbly, and the butter is broken up, stir in ½ cup of water with a rubber spatula until the water is absorbed and the dough starts to come together. If the dough is still dry and crumbly, add up to the remaining ¼ cup of water, 1 tablespoon at a time until the dough just starts to come together. Bring the dough together with your hands until it forms a soft and almost loose ball. Divide the pie dough into two pieces, one slightly larger than the other. You'll need the larger piece for the bottom crust. Transfer one piece to a sheet of plastic wrap and mold it into a rectangular shape, about 1-inch thick. Use the plastic wrap to help bring the dough together, if needed. Repeat with the remaining dough. Chill the dough in the refrigerator for at least 2 hours before using.

Step 3

To make the filling: In a very large bowl, toss the apple chunks with the lemon juice. Mix the sugar, cornstarch, cinnamon, nutmeg, allspice, and salt together in a medium bowl. Sprinkle the sugar-spice mixture over the apples and toss them well to coat; set aside.

Step 4

To assemble the slab pie: Preheat the oven to 375° F. Line the bottom of a 10×15×1-inch baking sheet or similarly sized jelly roll pan with a piece of parchment paper. If your pan is a little smaller than this (as mine was), don't worry - this recipe will still work fine; you'll just have a little extra dough leftover.

Step 5

Roll out the larger piece of dough on a well-floured surface with a rolling pin into a 18x13-inch rectangle. Transfer the piece to the pan and drape the edges of the dough over the sides of the pan while only gently pushing the dough down into the inside and corners of the pan. Slip the pan into the fridge or freezer while you roll out the second piece of dough into a 16x11-inch rectangle (you want to keep the dough in the pan as cold as possible).

Step 6

Remove the pan from the fridge/freezer and pour the apples and the juices over the dough in the pan - it may seem like way too many apples, but they will cook down. Drape the second sheet of dough over the apples. Trim the dough to where both top and bottom edges hang about ¾-inch over the edge of the pan. Seal up the edges tightly with your fingers.

Step 7

Brush the top of the dough with the heavy cream or egg wash. Using a sharp knife, slice a whole bunch of 1-inch slits in the top of the dough to allow the steam to escape during baking. Place the whole sheet on a larger baking sheet - there will likely be spillage that you'll want to catch on the large pan rather than the bottom of your oven (trust me).

Step 8

Bake for 40 to 45 minutes, until the top crust is a nice golden brown and the filling is bubbling through the holes in the crust. Cool the pan on a wire rack for at least 45 minutes before cutting and serving (see note below).