Prep: 20 mins Cook: 50-55 mins In lg bowl beat egg, stir in sour cream, sugar, flour, vanilla, and salt to blend thoroughly. Fold in apples and lemon peel, pour into pie shell. Bake 450, 10 mins. Reduce heat to 350, bake 25-30 mins until crust is golden brown. Sprinkle Streusel Topping evenly over pie. Bake 15 mins longer. Remove to rack to cool slightly. Serve immediately or cover and refrigerate. STREUSEL TOPPING; In sm bowl mix sugar, flour, cinnamon. With pastry blender or 2 knives, cut in butter to make a crumble mixture.