Preheat oven to 375 degrees F. Let piecrust stand at room temperature according to package directions. Unroll piecrust into a 9-inch pie plate. Ease piecrust into plate without stretching it. Crimp edge as desired.
If desired, sprinkle apples with lemon juice. In a large bowl, stir together sugar, flour, cinnamon, and nutmeg. Add apple slices; gently toss until coated.
Transfer apple mixture to the piecrust-lined pie plate. Sprinkle with Crumb Topping. To prevent overbrowning, cover edge of pie with foil. Bake for 40 minutes. Remove foil. Bake for 20 minutes more or until apples are tender and filling is bubbly. Cool on a wire rack. To serve warm, let pie cool at least 2 hours. Makes 8 servings.
In a medium bowl, stir together all-purpose flour and brown sugar. Using a pastry blender, cut in butter until mixture resembles coarse crumbs.