1 (1 pound) sweet potato
1/2 cup butter, softened
1 cup white sugar
1/2 cup milk
1/2 teaspoon ground nutmeg
1/2 teaspoon ground cinnamon
1 teaspoon vanilla extract
1 (9 inch) unbaked pie crust
Boil sweet potato whole in skin for 40 to 50 minutes, or until done. Cover pot and bring to a boil, then reduce to a simmer. Simmer about 50 minutes per pound or until tender.
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, cinnamon, and vanilla.
Beat on medium speed until mixture is smooth. Pour filling into an unbaked pie crust.
Bake at 350° F for 55 to 60 minutes, or until knife inserted in center comes out clean. Pie will puff up like a souffle, and then will sink down as it cools.