Whisk together the flour and salt in a large bowl. Cut in the butter with a fork, a pastry cutter, 2 butter knives, or your fingertips. It should look crumbly, with some pieces of butter the size of small peas.

Drizzle the water in a little at a time, mixing as you go (you can use a fork to mix, but it works best mixing with your fingertips). Add just enough water so it comes together to form a ball of dough (you may need more or less water).

Divide the dough into 2 equal parts. Roll each into a ball, flatten each ball slightly into a disk, wrap them in plastic wrap, and refrigerate until chilled, about 30 minutes.

Add all ingredients to a large bowl and whisk until well-combined.

Place 1 disk of dough onto a floured work surface. Working from the center out, roll the dough out to a rectangle about 14 by 10 inches. Use a 4-inch cookie or biscuit cutter (or a 4-inch bowl and a sharp paring knife) to stamp out as many circles as you can. Gather the dough scraps, re-roll the dough, and continue stamping out 4-inch circles until you run out of dough (you should get 16 to 18 pasties).

Put 1 1/2 tablespoons of filling in the center of each dough circle. Lightly brush egg wash on the outer half of dough on each, and fold the pasty over onto itself with the egg wash side facing the side with no egg wash (this will help the pastries stick together).

Transfer the pasties to a large baking tray lined with parchment paper or a silpat liner. Transfer the whole tray to the fridge to chill for 15 minutes (to yield the flakiest crust!).

Preheat the oven to 400F.

Use a fork to crimp the outside of each pasty (to help it stay sealed and stick together). Lightly brush the top of each pasty with egg wash. Use a sharp paring knife to cut 3 small slits in the top of each pasty (so steam can escape).

If desired, sprinkle cinnamon sugar on top.

Bake until the pasties are puffed, golden, and flaky, about 15 to 20 minutes.