• Put the butter in a small bowl and place it in the freezer. Fill a medium liquid measuring cup with water and add plenty of ice. Let the both the butter and the ice water sit for 5 to 10 minutes.
• In the bowl of a stand mixer fitted with a paddle, mix the flour, sugar, and salt on low until combined. Add half of the chilled butter and mix on low until the butter is just starting to break down, about 1 minute. Add the rest of the butter and continue mixing until the butter is broken down and in various sizes (some butter will incorporated into the dough, some will still be a bit large, but most should be about the size of small peas). Stop the mixer and use your hands to check for any large pieces of butter that didn’t get mixed or any dry patches of dough on the bottom of the bowl; break up the butter and incorporate the dry flour as best you can. With the mixer running on low, slowly add water a few tablespoons at a time and mix until the dough starts to come together but is still quite shaggy.
• Dump the dough out on a lightly floured work surface and flatten it slightly into a square. Gather any loose/dry pieces that won’t stick to the dough and place them on top of the square. Gently fold the dough over onto itself and flatten again. Repeat this process 3 or 4 times, until all the loose pieces are worked into the dough. Be very gentle with your movements, being careful not to overwork the dough. Flatten the dough one last time into a rectangle and cut into 2 pieces. Form the pieces into 6-inch discs and wrap in plastic wrap and refrigerate for 30 minutes before using.
• (For the fold-over pie crust shown above, instead of dividing the dough into two pieces, pinch off one-quarter of the dough, and save for another use. Pat the rest of the dough into a disc, and wrap with plastic until ready to use.)

For the Slab Pie Filling

• Combine cherries, grated apple, 1/2 cup of sugar, and salt in a large bowl. Let sit 30-45 minutes at room temperature.
• Strain the sugary juice from the fruit into a medium saucepan (you should have at least ½ cup of juice). Return the fruit to the large bowl. Add 1/4 cup granulated sugar to the juices in the pan and bring to a boil over medium heat. Simmer until reduced to a scant 1/2 cup, about 5-6 minutes, shaking the pan occasionally to stir. Remove from the heat and whisk in the butter. Stir in the kirsch and vanilla, then the heavy cream. Set aside to cool slightly.
• Sprinkle the cornstarch, lemon juice, and cinnamon over the cherries and toss to coat. Pour the slightly cooled fruit juice mixture over the fruit and stir gently.

To Assemble and Bake the Cherries + Cream Slab Pie

• Lightly flour a large sheet of parchment paper, and roll one piece of dough into a 17 by 13-inch rectangle. Repeat with the second piece of dough. Using the parchment paper, transfer one rectangle to a 13 by 9-inch jelly roll pan or quarter sheet pan. Press the dough into the pan; discard the parchment. Pour the filling on top of the dough and spread into an even layer. Using the parchment paper, place the second rectangle of dough on top of the filling; discard the parchment. Trim the dough overhangs to 1 inch past the lip of the pan. Pinch the dough together and tuck it under itself. Crimp the edges and cut several x-shaped vents across the top of the dough. Place the pan in the freezer for about 20 minutes while the oven is preheating. You want the crust to be nice and firm before you bake it.
• Adjust an oven rack to the lowest position. Preheat oven to 425°F. Place a baking sheet large enough to hold the jelly roll pan on the oven rack (the preheated baking sheet helps crisp the bottom of the pie crust and catches any leaks and drips).
• When ready to bake, brush the top of the slab pie with egg wash and sprinkle with 1 or 2 tablespoons of granulated sugar. Put the pie plate on the preheated baking sheet and bake 25 minutes. Reduce the oven to 375ºF and bake 40 to 50 minutes, until the crust is deep golden brown and the juices bubble.
• Transfer the slab pie in its pan to a wire rack and let cool at least 4 hours before serving.