Steps

• Preheat your oven to 375°F (190°C). Prepare a pie crust shield using aluminum foil.
• In a large bowl, combine ¾ cup of granulated sugar, 6 cups of fresh blueberries, and 6 cups of fresh peaches cut into 1-inch chunks. Add 2 tablespoons of cornstarch, 2 tablespoons of all-purpose flour, 1 teaspoon of ground cinnamon, and a pinch of salt. Mix in 1 tablespoon each of lemon juice and zest. Let sit for around 15 minutes.
• Roll out your all-butter pie crust until it's about ⅛ inch thick. Transfer it to your pie dish, pressing it into the bottom and sides. Trim excess dough, leaving about an inch for crimping.
• Using a slotted spoon, transfer the fruit mixture into your prepared pie crust, leaving juice behind. Smooth the filling evenly.
• Simmer the leftover fruit juices in a small saucepan over low heat for 1-2 minutes until thickened. Cool for 5 minutes before pouring over the fruit filling.
• Cover your pie with a lattice crust or preferred top. Beat 1 egg and 1 tablespoon of milk for the egg wash, brush over the top, and sprinkle coarse sugar if desired.
• Bake for 45-50 minutes until the filling is bubbling and the crust is golden brown. Tent with foil if browning too quickly.
• Cool completely on a wire rack for at least an hour before slicing.