Sour Cream Apple Pie

This is Mary Miller's recipe...

1 (9 inch) frozen unbaked pie shells (or your own recipe)
Pie filling
1 cup sour cream
2⁄3 cup sugar
2 tablespoons flour
1⁄4 teaspoon salt
1 teaspoon vanilla
1 egg
3 cups tart apples, peeled and sliced
Crumb topping
1⁄2 cup brown sugar, packed
1⁄3 cup flour
1⁄4 cup butter, room temperature
1⁄2 teaspoon cinnamon

Directions
Preheat oven to 400°F.
Beat together sour cream, sugar, flour, salt, vanilla and egg. Add apples, mixing carefully to coat well.
Pour filling into a pie shell and bake at 400 degrees for 25 minute.
While pie is cooking mix together all ingredients for crumb topping until the mixture resembles coarse crumbs. Don’t overmix.
Remove pie from oven and sprinkle with crumb topping. Bake for an additional 20 minutes.
Let cool for an hour before serving.