Sour Cream Apple Pie

1 egg
1 cup sour cream -- at room temperature
3/4 cup sugar
2 tablespoons flour
1/4 teaspoon vanilla
dash salt
2 1/4 cups finely chopped, peeled apples
1/4 teaspoon grated lemon peel
1 unbaked 9" pie shell

CRUMB TOPPING:
1/4 cup butter -- at room temperature
1/2 cup sugar
1/3 cup flour
3/4 teaspoon cinnamon

Preheat oven to 450°. Beat egg in a large bowl; blend in sour cream, sugar, flour, vanilla, and salt. Fold in apples and lemon peel. Pour into pie shell and bake 10 minutes. Reduce oven temperature to 350° and bake 30 minutes longer or until crust is golden brown. While pie is baking, prepare crumb topping: Cut butter into sugar, flour, and cinnamon. Sprinkle topping over pie and bake and additional 15 minutes. Serve warm or cool.