Notes from the Test Kitchen:
This has all the traditional apple pie goodness with the addition of scrumptious, crumbly topping! I like vanilla ice cream on mine, and I bet that some caramel sauce would be great too.
Heat oven to 400F. Unroll pie crust in 9-inch pie plate as directed on box for one crust filled pie. In a large bowl, beat sour cream, granulated sugar, flour, vanilla and egg with a wire whisk until well blended, stir in apples. Pour into crust lined pie plate.
Bake 15 minutes. Reduce temperature to 350F, bake 30 minutes longer.
Meanwhile, in a medium bowl, mix all topping ingredients except butter. With a pastry blender or fork, cut in butter until mixture looks like course crumbs. Refrigerate until ready to use.
Sprinkle topping over pie. Bake 20 to 25 minutes longer or until topping is golden brown. Cool completely on wire rack, about 2 hours. Cover and refrigerate any remaining pie.
high altitude (3500-6500 ft) in step 4, bake 25 to 30 minutes.