Blueberry and Peach Graham Galette

1.Process graham crackers, flour, 1 tablespoon sugar, and salt in a food processor until crackers become crumbs and mixture is combined. Add 10 tablespoons butter; pulse until mixture resembles coarse sand with some larger pieces remaining.
2.Add ice water by the tablespoon, pulsing after each addition, until evenly moistened and dough holds together when squeezed. Pat into 1"-thick disk and wrap tightly in plastic wrap. Chill at least 1 hour.
3.Toss peaches, blueberries, cornstarch, lemon zest, cinnamon, and 1/3 cup sugar in a large bowl, set aside. Cover a large sheet pan with parchment paper and preheat oven to 400 degrees.
4.Unwrap dough and roll out on a lightly floured surface to a 12" round. Transfer onto sheet pan. Arrange fruit on top, leaving a 1 1/4" border. Lift dough edges up and over fruit, pleating as needed. Chill in the refrigerator for 10 minutes.
5.In a small bowl beat the egg and then use it to brush the top of the pastry then sprinkle turbinado sugar on top of the pastry. Dot filling with 2 tablespoons butter.
6.Bake until fruit is softened and crust is deep golden brown, about 40-50 minutes. Serve warm or at room temperature.