Preheat the oven to 400°F. Line a baking sheet with parchment paper. Set aside.
Roll out the pie crust on a lightly floured surface into a 14-inch circle, about ⅛-inch thick. Transfer it to the parchment-lined baking sheet and refrigerate while preparing the filling.
In a medium bowl, combine the peaches, granulated sugar, cornstarch, and cinnamon. Gently toss to coat the peaches evenly. Let sit for about 10 minutes to allow the juices to develop.
Remove the chilled pie crust from the refrigerator. Spoon the peach mixture into the center of the dough, leaving a 2-inch border.
Fold the edges of the dough over the filling, pleating as needed to form a rustic crust.
Brush the exposed crust with the beaten egg. Then, sprinkle with turbinado sugar.
Bake for 30–35 minutes, or until the crust is golden brown and the filling is bubbling. If the edges brown too quickly, tent them with aluminum foil.
Let the galette cool for at least 10 minutes before serving.
Drizzle with honey and top with vanilla ice cream, if desired.