- Basic Sweet Piecrust 
- 2 pounds fresh rhubarb, trimmed and cut into 1-inch-thick pieces
- 2 pounds McIntosh apples (6 to 8 apples), cored, peeled, and each cut into 12 equal slices
- 1 cup granulated sugar
- 1 cup packed light brown sugar
- 1/4 cup cornstarch
- 2 tablespoons fresh lemon juice
- 2 tablespoons Calvados, kirsch, or Cognac
- 1 cup bleached all-purpose flour
- 1 cup chopped walnuts
- 4 tablespoons (1/2 stick) unsalted butter, cut into 1/2-inch pieces and chilled
- 1 teaspoon ground cinnamon
- Pinch of freshly grated nutmeg
- Preheat the oven to 350?F.
- Roll out the dough on a lightly floured work surface into an 11-inch round about 1/8 inch thick. Transfer the dough to a 9-inch pie pan. Trim off any overhanging dough to make a 1/2-inch-wide overhang around the edge of the pan. Flute the edges of the dough with your fingertips.
- Mix the rhubarb, apples, sugar, 1/2 cup of the brown sugar, the cornstarch, lemon juice, and Calvados in a large bowl and toss to coat the fruit evenly. Pour into the piecrust.
- Combine the flour, walnuts, the remaining 1/2 cup brown sugar, the butter, cinnamon, and nutmeg in a medium bowl. Mix well with your fingertips until the mixture resembles coarse crumbs. Sprinkle evenly over the filling.
- Bake until the topping is golden brown and the juices are bubbling, 35 to 40 minutes. Cool on a wire rack for at least 15 minutes before serving.
- Serve warm or cooled to room temperature.