Gather the ingredients.
Place whole sweet potato in pot and cover with water; bring to a boil. Boil until tender when pierced with a fork, 40 to 50 minutes.
Preheat the oven to 350 degrees F (175 degrees C). Remove sweet potato from the pot and run under cold water. Remove and discard skin. Break sweet potato flesh apart and place in a bowl. Add butter and mix with an electric mixer until well combined.
Add sugar, milk, eggs, nutmeg, cinnamon, and vanilla; beat on medium speed until mixture is smooth.
Pour filling into unbaked pie crust.
Bake in the preheated oven until a knife inserted in the center comes out clean, 55 to 60 minutes. Cool completely before serving.
