Heat oven to 350° F. Place the butter on a rimmed baking sheet and transfer to oven until melted.
Meanwhile, peel the sweet potatoes and cut them into 1-inch chunks. Add with the remaining ingredients and toss to combine. Roast, stirring occasionally, until tender, about 45 minutes.
Tip: You can use spiced nuts (store-bought or homemade) in place of plain.