Prepare the Dough. In a food processor, combine the flour, sugar, and salt. Pulse to combine. Add the cold, cubed butter and pulse until the mixture resembles coarse crumbs. Slowly add ice water, one tablespoon at a time, and pulse until the dough just comes together. Shape the dough into a disk, wrap it in plastic wrap, and refrigerate for at least 30 minutes.
Make the Filling. In a bowl, gently toss the sliced peaches with granulated sugar, cornstarch, vanilla extract, lemon zest, and a pinch of salt. Allow the mixture to sit for about 10-15 minutes to let the flavors meld.
Roll Out the Dough. On a lightly floured surface, roll out the chilled dough into a rough circle, about 12-14 inches in diameter.
Prebake for the Best Texture. Preheat the air fryer to 350°F.Transfer the rolled-out dough to a piece of parchment paper. Air fry for 5 minutes to begin baking the dough.
Assemble the Galette. Remove the undercooked dough from the air fryer. Arrange the peach slices in the center of the dough, leaving a border of about 2 inches. Gently fold the edges of the dough over the peaches, creating pleats as you go.
Egg Wash and Sugar Sprinkle. Brush the edges of the dough with beaten egg for a golden finish. Sprinkle turbinado sugar over the egg-washed edges.
Air Fry. Carefully transfer the parchment paper with the galette onto the air fryer basket. Air fry the galette for about 18-20 minutes or until the crust is golden brown and the peaches are tender.
Serve and Enjoy. Allow the galette to cool slightly before slicing.