In a large bowl, mix together the flour, sugar and salt. Using a box grater, grate the cold butter atop the flour mixture. Working quickly, and using your hands, break the butter bits into the flour until they're evenly distributed and resemble the size of small peas.
Add 3/4 cup of water and mix. The mixture will be shaggy at this point. From here, add 1 tablespoon of water at a time until the dough comes together (I usually need to add 3 to 4 tablespoons). Flour your counter and dump the dough onto it. Knead a few times more until it comes together. Divide the dough by setting aside 1/3 of the dough (eye ball this measurement; this will act as the bottom of the pie, you want more for the top). Forming two discs, one smaller than the other. Wrap the discs in plastic wrap and transfer to the refrigerator to chill for at least 1 hour, ideally overnight.
Remove the first disc of dough from the refrigerator and allow to come to room temperature for 10 minutes. Liberally flour your work surface and rolling pin. Begin to roll the dough, being sure to rotate it every so often to avoid sticking, to a 13x10inch rectangle. Use your quarter baking sheet as a guide. Wrap the dough around the rolling pin and unroll it over the baking sheet. Gently fit the dough into the bottom and up the sides. Trim the dough around the pie tin, leaving a 1-inch overhang. Add your filling and transfer the pie to freezer while you roll out the second disc of dough.
Remove the second disc of dough from the refrigerator and repeat the rolling process as you did with the first disc. You have a couple of options, I chose to do an intricate thick lattice meets braided situation. For this, I rolled about a quarter of the dough into 7x9 inch rectangle. I sliced that into thick strips and placed them atop the pie. I transferred it to the fridge while I worked on the braids.
To make the braids, I rolled the dough into a big rectangle and sliced thin strips with a sharp knife. I took three of the strips and braided away. I continued this process until I was stressed and got through the dough. I then latticed the big strips with the thin braids. My biggest advice is that the freezer is your friend. If the dough ever gets too soft, transfer it to the fridge on a cutting board. Tuck the edges under or over and then crimp the edge all the way around the slab pie. Put it in the freezer to chill for 30 minutes. This will eliminate the possibility of shrinkage. Preheat the oven (see below for more instructions) and brush the entire thing with egg wash and sprinkle with turbinado.