In a medium bowl, whisk together the flour, sugar, and salt. Cut in the butter until it resembles coarse crumbs. Gradually add cold water, stirring until the dough forms. Shape into a disk, wrap in plastic, and refrigerate for 1 hour.

Preheat your oven to 400°F (200°C). Wash, peel, and slice the peaches into wedges. Toss the peach slices with brown sugar, cinnamon, a pinch of salt, and cornstarch until evenly coated.

On a lightly floured surface, roll out the chilled dough into a 12-inch round. Transfer the dough to parchment paper on a baking sheet. Brush the surface with beaten egg white and spoon the peach filling in the center. Fold the crust edges up and over the filling.

Whisk together the egg yolk and milk to create an egg wash. Brush this mixture over the folded crust edges and sprinkle turbinado sugar on top. Bake for 30-35 minutes, until the crust is golden brown and the peaches are bubbling.

Once baked, let the Peach Crostata cool on a wire rack for about 2 hours. Slice and serve it warm or at room temperature, optionally paired with vanilla ice cream.