Our reader Ginny Kelly from Point Lookout, New York, got this recipe from her mother, who offered this advice: "Just tidy up the kitchen and keep an eye on the oven. When you're finished, the pie will be done."
Preheat oven to 425 degrees. In a large bowl, whisk together sugar, tapioca, and salt. Add peaches, blueberries, and lemon juice and toss to combine; let sit 15 minutes. Lightly flour a rolling pin and work surface and roll out half the dough to a 12-inch round. Place in a 9-inch glass pie plate and brush with egg white. Pour in fruit filling and dot with butter.
Roll out remaining dough to a 12-inch round and place over fruit filling. Trim excess and crimp edges to seal. In a small bowl, lightly beat egg yolk with 1 tablespoon cold water. Brush top of dough with egg yolk mixture. With a paring knife, cut several small slits on top to vent. Set on a rimmed baking sheet and bake until crust is deep golden brown and juices are bubbling, about 50 minutes. (Tent loosely with foil if crust browns too quickly.) Let pie cool completely on a wire rack, about 3 hours.
This pie pairs peaches and blueberries to make the most of summer's sweet bounty.