3 1/2 cups (375 grams) flour (you can swap out a a quarter of the amount for whole wheat if you like)
1/2 teaspoon coarse salt
3 sticks (1 1/2 cups) unsalted butter, cold, cut into pats
~1/3 cup ice cold water, as needed
1 1/2 pints strawberries (I started with two, but snacked heavily, and the amount worked well)
1/4 cup sugar (mine were crazy sweet, so I used less)
1 generous tablespoon tapioca starch
1 egg, beaten lightly with a splash of water (aka the egg wash)
coarse sugar and a few pinches salt for sanding
To make the crust (this can be done the day or so before): Stir together the flour and salt in a large bowl. Add the butter, and the press with the heel of your hand to flatten the pats of butter into flour-coated flakes. Stir the mixture, turning it from the bottom, then press again. Repeat the process until the pats gradually all turn into fat flakes (and some crumbs, as the flakes break apart). You'll be rolling this out a few times, so better to under-mix than over-mix now. Form a well in the middle and sprinkle in the water, using your fingertips to mix it into the flour and butter, until it all comes together into a cohesive ball. Again, you'll be rolling this out a few times, so it needn't be smooth, but it should come together. Add more water is needed. Once you can form a ball, place it in plastic wrap or a plastic bag, and refrigerate for at least half an hour.
When the dough has chilled and relaxed, lightly flour a counter top. Roll out the dough into a long rectangle, then fold up in thirds, like a letter. Rotate the dough 90°, so the seam is on the other side, and repeat the process three more times. This builds in nice flaky layers, almost like a rough puff pastry. When you've finished the final roll and fold, divide the dough in half, and again cover and chill for half an hour.
When you're ready to make your handpies: Preheat your oven to 400° Fahrenheit. Wash and chop your berries (somewhat small — your hand pies are only a few inches), and toss with the sugar and tapioca starch in a large bowl. Set aside. Have some baking sheets at the ready (lining with parchment makes things easier), and take half the dough out of the fridge for a few minutes to take the chill off.
Lightly flour a countertop, and roll out one of the dough halves into a 9-inch x 18-inch rectangle. Trim off the edges to square the dough, and then cut the dough into three-inch squares. Brush half of the squares lightly with the egg wash (for the bottoms), and cut small little vents in the other half (I favored a simple plus sign, but if you have little cutters or are feeling fancy, go nuts). Stir the filling and place about a tablespoon of it (leaving any excess juices behind) on one of the bottoms. Place one of the tops over it, and crimp with a fork to seal the edges. Place on cookie sheet. Got a sense of how it works and how much filling you can accommodate? Good. Repeat with the remaining dough and filling. Brush the finished hand pies with egg wash again, then give a generous paving of coarse sugar (and just a wee sprinkling of salt) over the top. Bake until the pastry begins to brown and thick juices bubble up, ~20 minutes. Let cool slightly, then enjoy. Without sharing.