2 ½ cups or 300 grams all-purpose flour
12 tablespoons or 169 grams unsalted butter, cold, cut into 1/2-inch cubes
1 teaspoon kosher salt
Yolk of 1 egg, beaten
1 teaspoon cider vinegar
¼ cup water, from 3/4 cup ice water
White of 1 egg, beaten
Pinch granulated sugar
6 or 7 ripe peaches, peeled and sliced, approximately 5 cups
2 tablespoons lemon juice
1 cup granulated sugar
¼ cup or 30 grams all-purpose flour
Pinch of ground nutmeg
Make the pie dough. Using your fingertips or the pulse function of a food processor, blend together the flour, butter and salt until the mixture resembles a coarse meal. There should be pebbles of butter throughout the mixture.
Add egg yolk and vinegar to 1/4 cup ice water, and stir to combine. Drizzle 4 tablespoons of this mixture over the dough, and gently stir or pulse to combine. Gather a golf-ball-size bit of dough, and squeeze to combine. If it does not hold together, add a little more of the liquid, and stir or pulse, then check again. Repeat as necessary.
Turn the dough out onto a lightly floured surface, and gather together into a rough ball. Divide the ball in half with a knife or a pastry scraper, then divide each portion in half again, and again, to create 8 portions. Using the heel of your hand, flatten each portion of dough once or twice to expand the pebbles of butter, then gather the dough together again in one ball. Divide this ball in half.
Flatten each ball into a 5- or 6-inch disc, one slightly larger than the other. Wrap the discs in plastic wrap, and place in the refrigerator for at least 60 minutes.
Preheat oven to 425. Make the pie filling: Combine sliced peaches, lemon juice, sugar and flour in a large bowl, and gently mix to combine. Set aside.
Take the larger of the pastry discs out of the refrigerator, roll it out on a lightly floured surface and place in a 9-inch pie plate. Add the peaches. Sprinkle them with the ground nutmeg.
Roll out second disc of pastry. Place on top of filling. Wet edges of the bottom pastry disc with some cold water. Trim pastry, pinch bottom and top edges together and cut a few slits to allow steam to escape from the pie. Brush the egg white on the top, particularly around the edges, and sprinkle with a pinch of granulated sugar.
Bake the pie for 15 minutes, then reduce heat to 375. Cook until peaches bubble and pastry is golden, approximately 45 minutes to an hour.