Sour Cream Apple Pie

1 cup sour cream
1 egg
3/4 cup granulated sugar
2 tablespoons all-purpose flour
1/4 teaspoon salt
1 teaspoon vanilla extract
2 1/2 cups diced apples, peeled
1 unbaked 9-inch pie crust

Crumb Topping:
1/2 cup brown sugar
1/4 cup butter
1/3 cup all-purpose flour
1 teaspoon cinnamon

Beat cream and egg together. Add flour, sugar, salt and vanilla extract. Mix until smooth. Stir in apples. Bake at 400 degrees F for 25 minutes. Remove from oven and spread with crumb topping. Bake 20 more minutes. Mix until crumbly.