1 unbaked 9-inch unbaked pie crust
1/2 cup all purpose flour
Preheat oven to 400 degrees.
In a large bowl stir together the egg, sour cream, granulated sugar, 2 Tbsp. flour, vanilla, and salt. Stir in chopped apples. Pour the mixture into the unbaked pie crust. Cover edge of pie crust with foil. Bake at 400 degrees for 25 minutes.
While pie is baking make streusel topping. In a small mixing bowl combine the 1/2 cup flour and the brown sugar. cut in butter until crumbly.
After the pie has baked for 25 minutes, remove foil from pie and sprinkle with streusel topping. Bake 20 more minutes, or until top is golden brown. Cool on wire rack. Refrigerate within 2 hours; cover for longer storage.