1Heat oven to 400°F. Unroll pie crust in 9-inch glass pie plate as directed on box for One-Crust Filled Pie. In large bowl, beat sour cream, granulated sugar, flour, salt, vanilla and egg with wire whisk until well blended; stir in apples. Pour into crust-lined pie plate.
2Bake 15 minutes. Reduce oven temperature to 350°F; bake 30 minutes longer.
3Meanwhile, in medium bowl, mix all topping ingredients except butter. With pastry blender or fork, cut in butter until mixture looks like coarse crumbs; refrigerate until ready to use.
4Sprinkle topping over pie. Bake 20 to 25 minutes longer or until topping is golden brown. Cool completely on cooling rack, about 2 hours. Cover and refrigerate any remaining pie.