Preheat oven to 350 degrees F (175 degrees C).
Boil sweet potato whole in skin for 50 to 55 minutes, or until done.
Run cold water over the sweet potato, and remove the skin.
Break apart sweet potato in a bowl.
Add butter and mix well with mixer.
Stir in sugar, milk, eggs, nutmeg, and cinnamon.
Beat on medium speed until mixture is smooth.
Pour filling into an unbaked pie crust.
Bake at 350 degrees F (175 degrees C) for 55 to 60 minutes, or until knife inserted in center comes out clean.