In a large mixing bowl, combine all-purpose flour, granulated sugar, and kosher salt. Using a pastry cutter or your fingertips, rub in the unsalted butter until the mixture resembles coarse crumbs with pea-sized butter pieces. Gradually add cold water, mixing until the dough just comes together. Shape into a disk, wrap in plastic, and refrigerate for at least 1 hour to chill.

As the dough chills, preheat your oven to 400°F (200°C). Prepare a baking sheet lined with parchment paper.

On a lightly floured surface, roll out the chilled dough into a 12-inch circle, about 1/8 inch thick. Transfer the dough to the prepared parchment-lined baking sheet. Brush the center with beaten egg white, leaving a 2-inch border around the edges.

Wash, peel, and slice the large yellow peaches. In a mixing bowl, toss the peach slices with light brown sugar, ground cinnamon, a pinch of salt, and cornstarch until evenly coated.

Layer the peach filling in the center of the dough, leaving the 2-inch border free. Gently fold the edges of the dough over the fruit, creating pleats as you go around. Brush the folded edges with the egg wash and sprinkle turbinado sugar.

Bake in the preheated oven for 30-35 minutes until the crust is golden brown and the peaches are bubbling.

Allow it to cool on a wire rack for at least 2 hours. Slice the crostata and serve warm, optionally with ice cream or whipped cream.