Combine flour, sugar, and salt in a large bowl, then cut in the cold butter until coarse crumbs form. Gradually add ice water, mixing until the dough comes together, then flatten into a disk, wrap, and chill for at least 30 minutes.

Prepare the peaches by peeling and slicing them, then gently toss them with sugar, cornstarch, lemon juice, vanilla extract, and cinnamon in a bowl.

Roll out the chilled dough into a 12-inch circle on a floured surface, then transfer it to a parchment-lined baking sheet and arrange the peach mixture in the center, leaving a 2-inch border.

Fold the dough edges over the peaches, pleating as needed, then brush the crust with the beaten egg and sprinkle with turbinado sugar.

Bake at 375°F (190°C) for 45-50 minutes, or until the crust is golden brown and the filling is bubbly, then let it cool before serving.