How to Follow
In order to get the foundation ready: In a large, broad basin, place the flour. Equalize the sugar and salt. Scatter the flour over the butter bits. Use the index fingers of both hands to crack the butter into pea-sized bits. A robust pastry blender or two knives would also do the trick. I like working with my hands.
Using a rubber spatula, add half a cup of water until the mixture seems basically unchanged, slightly crumbly, and the butter has been chopped into tiny bits. When the dough starts to come together, it means the water has been absorbed. Keep mixing. Incorporate more water gradually until the dough starts to come together if it remains dry and crumbly. The dough should be mixed by hand until it forms a soft, somewhat loose ball. Make two somewhat larger pieces of pie dough by cutting the dough in half. The larger component is required for the base of the crust. Shape one half into a rectangle that is about 1 inch thick on top of a sheet of plastic wrap. If the dough isn't sticking together, use the plastic wrap. Repeat with the remaining dough. Allow the dough to cool in the refrigerator for a minimum of two hours before to its use.
In a large dish, combine the apple chunks with the lemon juice to make the filling. For the sugar mixture, in a medium bowl, combine the cornstarch, cinnamon, nutmeg, allspice, and salt. After coating the apples evenly with the sugar and spice mixture, set them aside.
Assembling the slab pie requires: Set the oven temperature to 375 degrees Fahrenheit. A baking sheet with dimensions of 10 by 15 inches and a depth of 1 inch should have parchment paper laid down on its base. This recipe will still work, even if your pan is little smaller than mine; you will just have more dough than you need.
Roll out the large ball of dough on a floured board into a rectangle that is 18×13 inches in size. After placing the dough in the pan, fold over the edges to seal it. Carefully push the dough into the pan's interior and corners. While you shape the second ball of dough into a rectangle measuring 16 by 11 inches, place the pan in the refrigerator or freezer to keep it cool.
Remove the pan from the refrigerator or freezer. Toss the dough in the pan with the apples and their juices. The apples will boil down and become much smaller, so don't be fooled by their appearance. Arrange the apples on top of the second dough ball. Trim the dough so that it stretches about three quarters of an inch beyond the pan on both sides. Tighten the edges by pressing down with your fingertips.
Coat the dough with a thick egg wash or heavy cream. Make many shallow incisions on top of the dough, about an inch apart, to release steam while it bakes. Spread the whole sheet out on a larger baking sheet; you'll collect any spills there instead of at the base of the oven.
After 40 to 45 minutes in the oven, you should see a beautiful golden brown crust and contents bursting through the crust gaps. Wait at least 45 minutes for the pan to cool on a metal rack before slicing and serving.
