Preheat the oven to 400 degrees.  Line a sheet pan with parchment paper.

Bring a medium pot of water to a boil.  Immerse the peaches for 15 seconds to 2 minutes, testing along the way, until the skins peel off easily with a small knife. (Riper peaches will be done sooner.)  Transfer the peaches to a bowl of cool water to stop the cooking and peel.  Cut one peach in ½-inch dice and set aside.  Cut the remaining peaches in ½-inch thick wedges and place them in a large bowl.

In a small saucepan, whisk together the ½ cup sugar, the cornstarch, orange zest, orange juice, and butter over medium heat and bring to a boil.  Add only the diced peach (not the wedges), return to a boil, then lower the heat and simmer for 2 to 3 minutes, stirring occasionally, until the liquid is thickened and translucent.  Combine the mixture with the wedged peaches and 1 to 3 tablespoons of the flour, depending on the juiciness of the peaches (more flour if the peaches are juicier).

Roll out half the pie dough on a floured board until it’s larger than a 9-inch pie plate. Ease the dough into the pie plate without stretching it at all. (If you stretch the dough, it will shrink back to the original size.) Cut off the excess dough around the edge of the pie plate with a small sharp knife. Pour the peach mixture into the pie shell.  Brush the edge of the dough with the egg wash. Roll out the remaining dough until it’s larger than the pie plate.  Cut 1-inch strips of dough and weave them together on top of the pie. Cut off the excess dough at the edge and crimp the crusts together with a fork. Brush the crust with the remaining egg wash and sprinkle generously with sugar. Place the pie on the prepared sheet pan and bake for 45 minutes to 1 hour, until the pastry is browned and the filling is bubbly.  Allow to cool and serve warm or at room temperature.