Bring a large pot of water to a boil over high heat. Cut out any dark spots or "eyes" from the sweet potatoes. Then, cut the potatoes in half and carefully place them in the boiling water. (see note)
Cover the pot with a lid and boil until potatoes are tender, about 20 minutes. Drain the water and let the potatoes rest until they're cool enough to handle.
While potatoes are cooling, add the heavy cream and butter to a medium saucepan. Place over medium heat and cook until the butter is melted and the cream is warmed through.
Once potatoes are cooled, use your hands to remove the skin. It will come off easily.
Add the potatoes, cinnamon, nutmeg, and brown sugar to the bowl of a stand mixer. Using the whisk attachment, whip the potatoes while drizzling in the warm cream and butter mixture. Continue beating until smooth and creamy.
Transfer to a serving bowl and sprinkle with cinnamon and chopped parsley for garnish. Serve warm.
Notes
If you prefer to peel the potatoes before boiling, rather than after, you can.