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.