With summery, bright fruit, this pie is a crowd- pleaser and pretty enough to be the centerpiece for a summer dinner party. The crust is tender, with a deeper flavor from the whole-wheat flour than you would get with a plain white-flour crust.
Place pastry flour, 3 tablespoons of the granulated sugar, and 1/2 teaspoon of the salt in bowl of a food processor. Add butter, and pulse until mixture resembles coarse meal, about 10 times. Add yogurt and water, and pulse until pea-size pieces of dough begin to come together and dough just begins to pull away from sides of bowl, about 20 times. Turn dough out onto a piece of plastic wrap, and shape into a 6-inch disk. Wrap tightly with plastic wrap, and chill 1 hour or up to overnight.
Preheat oven to 425F. Toss together peaches, blueberries, all-purpose flour, vanilla, and remaining 3 tablespoons granulated sugar and 1/4 teaspoon salt in a large bowl. Set aside.
Unwrap dough, and place on a large sheet of parchment paper. Dust top of dough lightly with all-purpose flour, and roll into a 15-inch circle. Transfer dough and parchment paper to a large baking sheet. Pour fruit mixture into center of dough, and spread over dough, leaving a 2-inch border around edges. Fold dough edges in toward filling. Brush dough edges with egg white, and sprinkle with turbinado sugar. Freeze 10 minutes.
Bake in preheated oven until filling is hot and bubbly and crust is golden brown, about 30 minutes. Let cool to room temperature, about 30 minutes.