Sweet and summery gluten free peach pie is bursting with fresh, juicy fruit and a touch of warming cinnamon, all tucked into a flaky gluten free crust.
In a large bowl, whisk the flours, sugar, and salt. Cut in the butter with a fork, then drizzle in the ice water 1 tablespoon at a time until the dough holds together when lightly squeezed. Separate the dough into two equal balls, wrap them in plastic, press them into discs, and chill them in the fridge for at least 30 minutes.
Make the Filling
In a large bowl, mix the chopped peaches with the granulated sugar, tapioca flour, lemon juice, and cinnamon together until thoroughly combined. Place the filling in the fridge until you're ready to assemble the pie.
Assemble
Preheat the oven to 425°F. Place a large baking sheet on the bottom oven rack to catch drips from the pie. Butter a 9-inch pie pan.
Dust a surface with oat flour and roll out one of the dough discs, keeping the second one in the fridge until you're ready to roll it out. Roll the dough into a circle 12 inches in diameter. Carefully fit the dough into the buttered dish. Pour the filling into the crust and dot it with the butter if using.
Remove the other disc dough from the refrigerator and roll it into a 12-inch diameter circle. Cut out strips of dough to make a lattice crust (6-8 strips). Thread the strips over and under each other on the top of the pie, then use your fingers to seal the strips to the edges of the bottom crust. Use a fork to make crimps around the edge of the pie. Brush the crust with 1 tablespoon of whole milk.
Place the pie in the oven and bake it at 425°F for 20 minutes, then reduce the temperature to 375°F and continue baking until the crust is firm and lightly browned and the filling is bubbling, about 1 hour.
Remove the pie from the oven and cool on a rack for 3-4 hours before serving.