Heat oven to 400° F.
Pierce each sweet potato several times with a fork. Place on a rimmed baking sheet, cover with foil, and roast until tender, about 1 hour. Remove from oven and let rest until cool enough to handle.
Using your fingers, carefully peel the sweet potatoes and place in the bowl of a food processor. Add the butter, maple syrup, salt, pepper, and nutmeg. Puree until smooth. Transfer to a serving bowl.