How to Make It
Bring a medium saucepan of water to a boil. Fill a bowl with ice water. Using a sharp paring knife, mark an X on the bottom of each peach. Add the peaches to the saucepan and blanch until the skins start to peel away, 1 to 2 minutes. Transfer to the ice bath and let cool completely. Peel, halve and pit the peaches and cut into 1/4-inch pieces; you should have about 2 cups. Wipe out the saucepan.
In the same saucepan, combine the peaches with all the remaining ingredients and bring to a boil. Cook over moderate heat, stirring occasionally, until thickened and syrupy, about 12 minutes. Scrape the filling into a small bowl; let cool to room temperature. Cover and refrigerate until cold, 2 hours.
In a large bowl, whisk the flour with the salt. Scatter the butter over the flour and, using your fingers, pinch it in until the mixture resembles very coarse crumbs, with some pieces the size of small peas. Stir in the ice water just until a dough forms. Turn out onto a lightly floured work surface and knead gently to form a ball. Pat into a 1-inch-thick round, wrap in plastic and refrigerate for 1 hour.
Preheat the oven to 450° and line a baking sheet with parchment paper. Cut the dough in half. On a lightly floured work surface, using a lightly floured rolling pin, roll out 1 piece of dough 1/8 inch thick. Using a 4-inch biscuit cutter, stamp out 6 rounds and transfer to the prepared baking sheet. Top with a layer of parchment paper. Gather the scraps and form into a ball; roll out again and stamp out 2 more rounds. Transfer to the baking sheet. Repeat with the second piece of dough. Refrigerate for 30 minutes.
Line 2 baking sheets with parchment paper. Working with 1 dough round at a time, brush the rim with the beaten egg. Spoon 2 teaspoons of the filling into the center and fold the round in half to enclose. Press the edge firmly to seal and transfer to a prepared baking sheet. Repeat with the remaining dough and filling, arranging the hand pies 2 inches apart on the sheets. Brush the tops with the remaining beaten egg and sprinkle with turbinado sugar. Using a paring knife, cut 2 small slits in each hand pie. Bake until puffed and golden brown, shifting the pans from top to bottom and back to front halfway through baking, 18 minutes. Transfer the hand pies to a rack and let cool slightly.