In a large bowl, combine the all-purpose flour, 1 tablespoon granulated sugar, and 1 1/2 teaspoons fine-grain sea salt. Using a box grater, grate the sticks of frozen unsalted butter directly over the flour mixture. Quickly work the butter into the flour with your hands until the mixture resembles small peas. Add 1/2 cup of ice-cold water and mix, then gradually add more water, 1 tablespoon at a time, until a shaggy dough forms and comes together. Lightly flour your counter, turn out the dough, and knead it just a few times until it comes together. Divide the dough into two discs, wrap each in plastic, and refrigerate for at least 1 hour (or overnight for best results). I find chilling the dough overnight gives it the best texture!

Let the chilled dough discs sit out for 10 minutes to soften slightly. Generously flour your work surface and rolling pin. Roll one disc into a 13-inch round, rotating as you go to avoid sticking. Use a 3-inch cookie cutter to cut out as many circles as possible (about 6 from the first roll). Gather and reroll scraps to cut 2 to 4 more circles. Place the cut dough circles on a parchment-lined baking sheet and refrigerate them. Repeat the process with the second disc. If you wish, use the back of a piping tip or a paring knife to cut small vents or decorative shapes in some of the circles for the pie tops.

While the dough chills, make the filling by combining the pitted and coarsely chopped sour cherries, 1/4 cup granulated sugar, 3 tablespoons tapioca flour, and 1/4 teaspoon sea salt in a bowl. Toss everything together to coat the cherries evenly. Let the mixture stand for a few minutes to allow the juices to start thickening, thanks to the tapioca flour.

Remove the chilled dough circles from the refrigerator. Brush each bottom dough circle with egg wash (use a beaten egg, though not specified, as it's a standard method). Place a scant teaspoon of cherry filling from Step 3 in the center of each circle. Cover with another dough circle (with vents if desired). Using the tines of a fork, press around the edges to seal. Trim any uneven edges for perfect circles if you wish. Return the assembled pies to the baking sheet, and freeze for 15–20 minutes until very firm before baking. I like to make sure the pies are very cold before they hit the oven for the best flaky result.

While the hand pies firm up in the freezer, preheat your oven to 425°F (220°C). Once the pies are very cold, place the baking sheet directly into the hot oven. Bake for 12 to 15 minutes, or until the tops are golden brown. Remove from the oven and allow pies to cool for a few minutes before enjoying.