Active time: 40 minutes Start to finish: 6 hours(includes making dough and cooling pie)
Ingredients
1 cup granulated sugar
3 tablespoons cornstarch
2 tablespoons quick-cooking tapioca
1/4 teaspoon salt
3 cups fresh blackberries (3/4 to 1 pound)
2 cups fresh raspberries (1/2 to 3/4 pound)
2 cups fresh blueberries (1/2 to 3/4 pound)
Pastry dough
1 large egg, lightly beaten
1 tablespoon sanding or granulated sugar
Special equipment: a 9-inch metal or glass pie plate (4-cup capacity)
Accompaniment: vanilla cream
Directions
Put a large baking sheet in middle of oven and preheat oven to 450°F.
Whisk together granulated sugar, cornstarch, tapioca, and salt, then toss with berries.
Roll out 1 piece of dough (keep remaining piece chilled) on a lightly floured surface with a lightly floured rolling pin into a 13-inch round and fit into pie plate. Trim edge, leaving a 1/2-inch overhang. Chill shell while rolling out dough for top crust.
Roll out remaining piece of dough on lightly floured surface with floured rolling pin into an 11-inch round.
Spoon filling into shell, then cover pie with pastry round and trim with kitchen shears, leaving a 1/2-inch overhang. Press edges together, then crimp edge decoratively. Brush top of pie with egg and sprinkle all over with sanding sugar. Cut 3 steam vents in top crust with a small sharp knife.
Bake pie on hot baking sheet in middle of oven 15 minutes, then reduce oven temperature to 375°F and continue to bake until crust is golden brown and filling is bubbling, about 45 minutes more.
Cool pie on a rack at least 3 hours before serving to allow juices to thicken slightly (filling will still be juicy).
