1. Place sweet potatoes in a large pan, cover with cold water and bring to boil over high heat. Reduce heat to low and simmer until potatoes are tender, about 45 minutes. Drain.
2. While potatoes are cooking, cut 4 oranges in half and carefully remove pulp and juice. Place orange halves in a large muffin pan to stand them up, or arrange in a large baking dish; set aside.
3. Preheat oven to 350ºF. Puree potatoes in a food processor until smooth. Add butter, chipotle and zest and juice of remaining orange; puree. Season with salt and pepper.
4. Pipe or spoon puree into orange shells and bake for 30 minutes.