Trim ends and roots from rutabaga, peel, and chop into chunks. Add to a large stockpot and cover with cold water. Bring to a boil and cook for 20-30 minutes, until easily pierced with a fork.
Drain, return to pot, and mash. Warm butter and cream, then mix into rutabaga along with parmesan. Continue to mash or use a hand mixer to mix until your desired consistency is achieved (it might not be as smooth as mashed potatoes).
Add salt and pepper to taste, and serve with additional butter and parmesan on top.