Peel cooked sweet potato and place into the bottom of a large bowl. Should be about 2 cups. Mash or stir until very smooth. Cream in butter and sugars.
Stir in the evaporated milk, vanilla, eggs spices, and salt. Scrape the sides of the bowl and stir again until the mixture is completely smooth and uniform. Pour into prepared pie shell and bake at 375 degrees for 45-60 minutes or until set.
Cool completely before serving. If making in advance, cover with plastic wrap and refrigerate. Serve with whipped cream and cinnamon, if desired.