Make the pie dough: In a large bowl, whisk 2 1/2 cups flour and 1 teaspoon salt. Cut in 1 cup cold unsalted butter (cubed) and 1/4 cup cold shortening until the mixture looks like pea-sized crumbs with some larger bits. Sprinkle in 6–8 tablespoons ice water, tossing with a fork until the dough just comes together.

Chill the dough: Divide into two disks, wrap tightly, and chill for at least 1 hour. Cold dough is key to a flaky crust.

Prep the peaches: Peel if desired. Slice peaches about 1/2-inch thick. You should have 6–7 cups. If your peaches are very juicy, blot lightly with a paper towel.

Mix the filling: In a large bowl, combine peaches with 1/2 cup granulated sugar, 1/4 cup light brown sugar, 1/4 cup cornstarch, 1 tablespoon lemon juice, 1 teaspoon vanilla, 1/2 teaspoon cinnamon, and a pinch of nutmeg. Toss gently and let sit 10 minutes to start releasing juices.

Heat the oven: Preheat to 425°F (220°C). Place a baking sheet on the middle rack to preheat. This helps set the bottom crust quickly.

Roll the bottom crust: On a lightly floured surface, roll one dough disk into a 12-inch circle. Fit into a 9-inch pie dish, leaving a slight overhang. Chill the lined dish while you roll the top crust.

Fill and dot with butter: Spoon the peach filling into the crust, scraping in any juices. Dot the top with 1–2 tablespoons small pats of butter.

Top crust or lattice: Roll the second disk into a 12-inch circle. Either lay it on top and cut several slits for steam, or cut strips for a lattice. Trim excess and crimp edges to seal.

Egg wash and sugar: Brush the top with a beaten egg mixed with 1 tablespoon water. Sprinkle with coarse sugar if you like extra sparkle and crunch.

Bake hot, then lower: Place the pie on the preheated baking sheet. Bake at 425°F for 20 minutes. Reduce heat to 375°F (190°C) and bake another 35–45 minutes, until the crust is deep golden and the filling bubbles thickly through the vents.

Shield if needed: If the edges brown too quickly, cover them with foil or a pie shield during the last 20–25 minutes.

Cool completely: Let the pie cool at least 3–4 hours on a rack. This allows the filling to set, so slices hold together.

Serve: Slice with a sharp knife. Serve warm or at room temperature, plain or with vanilla ice cream or whipped cream.