Peel and chop sweet potatoes into 3 cm chunks.
Dice onion into similar sized pieces.
In a large stock pot or dutch oven add sweet potatoes, onion, broth and butter. Bring to a boil over high heat and then cover, turn to low and simmer about 20 minutes until sweet potatoes are soft.
Puree – with hand blender or blender or food processor. If soup is too thick you can add more broth or water. Add nutmeg, pepper and salt if needed.