Crust: Combine the graham cracker crumbs, flour, brown sugar, and melted butter. Press into the bottom of a pie pan and Bake 10 minutes at 350 degrees. Filling: Blend well until very smooth, peanut butter, cream cheese, burnt sugar flavoring (optional), powdered sugar, and milk. Add 1 large carton cool whip, blend and pour into shell and freeze at least 24 hours.