Mix crust ingredients and press into a 9-inch pie pan, reserving 3 tablespoons of the crumb mixture to sprinkle on top. Combine all filling ingredients except the sour cream, beating until smooth. Fold in the sour cream by hand. Pour into the crust. Sprinkle with topping. Bake at 375 degrees F until set, about 35 minutes. Cool and chill about 4 to 5 hours.