Dice the cold butter and return it to the fridge. In a food processor, pulse the flour, salt, and sugar to combine. Add the butter and shortening, and pulse 8-10 times until the mixture looks like pea-sized crumbs. With the machine running, pour in the ice water and pulse just until the dough starts to clump together.

Turn the dough out onto a floured surface and gather it into a ball. Wrap in plastic and refrigerate for 30 minutes. (If it chills longer, it may become too firm to roll.)

On a floured counter, cut the dough in half. Roll one half into a circle about 12 inches across. Carefully transfer it to a 9-inch pie dish, letting the edges overhang. Trim the excess with a sharp knife. Return the other half to the fridge.

Preheat the oven to 400°F. Line a baking sheet with parchment paper.

Peel and slice all but one peach, placing them in a large bowl. (To peel easily, blanch the peaches in boiling water for 15 seconds to 2 minutes, then plunge into cold water; the skins will slip off.) Dice the remaining peach and set aside.

In a small saucepan, whisk together the sugar, cornstarch, orange zest, orange juice, and butter. Bring to a boil over medium heat. Add the diced peach, return to a boil, then lower the heat and simmer for 2-3 minutes, stirring occasionally, until the syrup thickens slightly.

Pour the hot syrup over the sliced peaches and stir in 1-2 tablespoons of flour to thicken the filling further. Pour the mixture into the prepared crust. Brush the edges of the crust with some egg wash.

Roll out the remaining dough into a 12-inch circle. Cut it into 1-inch wide strips and weave a lattice over the filling. Press the edges together with a fork, trimming any excess dough.

Brush the entire lattice with egg wash, getting into all the nooks. Sprinkle generously with sugar. Place the pie on the prepared baking sheet and bake for 45 minutes, rotating halfway, until the crust is golden brown and the filling is bubbly. Cover the edges with foil if they brown too quickly.

Cool the pie on a rack. Serve warm or at room temperature.