Martha shows Rachael Ray how to bake a beautiful apple-blackberry pie for the holidays.
Whisk together granulated sugar, cornstarch, cinnamon, and salt in a large bowl. Add apples and blackberries, and toss to coat. Pour filling into prepared piecrust, and dot with butter.
Preheat oven to 400 degrees with rack in lowest position. Meanwhile, brush rim of piecrust with egg wash. Arrange dough leaves over filling, creating a spiral from the edge into the center, overlapping leaves slightly to cover pie but leaving some openings. Lightly brush tops of leaves with egg wash as you work, to help them adhere. Once filling is covered with leaves, lightly brush top of entire pie with egg wash. Sprinkle with sanding sugar. Freeze for 30 minutes.
Place pie on a parchment-lined rimmed baking sheet. Bake until crust is golden, about 20 minutes. Reduce heat to 350 degrees. Bake pie, rotating sheet halfway through, until juices are bubbling in the center and crust is golden brown, 1 hour and 45 minutes to 1 hour and 55 minutes more. Transfer to a wire rack, and let cool completely. (Pie can be stored at room temperature for up to 1 day.)