Blend sour cream,1/2 cup brown sugar, eggs, 2 tablespoon flour, vanilla, lemon juice, and salt in a large bowl with a whisk. Add apples and stir until well coated. Spoon into pie crust.
Stir together oats, remaining 3/4 cup flour, remaining 1/4 cup brown sugar, and cinnamon. Place butter and peanut butter in a microwaveable bowl on high 30 seconds or until butter is melted. Add to oat mixture; blend until crumbs are formed. Sprinkle crumb mixture over apples.
Bake 55-60 minutes or until apples are tender and topping is golden brown. Cool completely and store left over pie in refrigerate leftovers.