In a large mixing bowl, combine all-purpose flour, granulated sugar, and kosher salt. Cut in cold unsalted butter using a pastry cutter or your fingers until the mixture resembles coarse crumbs. Gradually add cold water and mix just until the dough starts to come together. Form the dough into a disk, wrap it in plastic wrap, and refrigerate for at least 1 hour to allow the flavors to meld.

Preheat your oven to 400°F (200°C). On a lightly floured surface, roll out the chilled dough to about a 12-inch round. Transfer the dough onto a parchment-lined baking sheet, then brush the surface with egg white to create a barrier. Refrigerate the rolled dough while you prepare the filling, ensuring it stays cold and manageable.

Peel and slice the ripe yellow peaches into thin wedges and place them in a mixing bowl. Toss the peach slices gently with light brown sugar, cinnamon, a pinch of salt, and cornstarch until they are well-coated. Arrange the delicious peach mixture evenly over the center of the dough, leaving a generous 1-1.5-inch border free of fruit to fold the edges.

Fold the edges of the dough over the peach filling, overlapping it slightly as you go for a rustic look. Brush the exposed dough edges with egg wash for a golden finish and sprinkle turbinado sugar over the crust for added crunch. Bake your peach crostata for 30-35 minutes or until the crust is golden brown and the peaches are bubbly.

Once baked, remove the peach crostata from the oven and let it cool on a wire rack for at least 2 hours. This cooling time allows the juices to set, making it easier to slice. Serve it warm or at room temperature.