Step 1

Pulse flour, sugar, and salt in a food processor just to combine. Add butter and pulse until most of the butter is pea-size with some larger pieces throughout. Drizzle vinegar and ⅓ cup ice water over and pulse, scraping down sides once, just until dough comes together in clumps and there are no large pockets of flour. (Alternatively, whisk flour, sugar, and salt in a large bowl and use a pastry cutter to work in butter, then mix in vinegar and water with a rubber spatula.)

Step 2

Transfer dough clumps to a clean work surface. Using a bench scraper, bring dough together (it will still look quite sandy and you might be tempted to add more water—don’t!) and gently pat into a 1"-thick rectangle. Using bench scraper, fold dough in half, then gently pat down again into a 1"-thick rectangle. Fold and pat down dough 2 more times (it should be fairly smooth at this point). Divide dough in half, flatten into disks, and wrap each tightly in plastic. Chill at least 2 hours and up to 3 days.

Step 3

Let 1 disk of dough sit at room temperature 5 minutes to slightly soften. Roll dough on a floured surface to a 12"-diameter round. Transfer dough to pie dish; lift up edges and allow dough to slump down into dish. Trim, leaving about 1" overhang. Chill while you prepare the filling.

Step 4

Gently toss peaches, cornstarch, lemon juice, brandy (if using), vanilla extract, orange zest, salt, nutmeg, ⅔ cup (133 g) sugar, and 1 Tbsp. flour in a large bowl to coat; set filling aside.

Step 5

Roll second disk of dough on a floured surface to a 12"-diameter round. Scrape reserved filling, including juices, into pie crust; dot filling with butter. Top with remaining dough round then press crust edges together and fold over to seal; crimp edges.

Step 6

Place pie on a foil-lined rimmed baking sheet and chill in freezer 20 minutes (this helps the crust to become extra flaky).

Step 7

Meanwhile, place a rack in middle of oven and preheat to 400°.

Step 8

Beat egg with 1 Tbsp. water in a small bowl. Mix cinnamon and remaining 2 Tbsp. sugar in another small bowl. Brush pie crust with egg wash, then sprinkle with cinnamon sugar. Cut slits in top of crust to make a large X.

Step 9

Bake pie on baking sheet 15 minutes. Reduce oven temperature to 350° and continue to bake pie, tenting with foil halfway through if crust is browning too quickly, until juices are thickened and bubbling in the center and crust is deep golden brown (check bottom if you can), about 1½ hours. Transfer pie to a wire rack and let cool at least 3 hours before serving.

Step 10

Serve slices of pie with scoops of vanilla ice cream if desired.Do ahead: Pie can be baked 3 days ahead. Cover tightly and chill.