Cook the Vegetables. Put the diced rutabaga and carrots in a medium saucepan. Cover with water and about 1 teaspoon of salt, and bring to a boil. Cover the pan and reduce the heat to medium-low; continue cooking for about 20 minutes or until the vegetables are tender. Drain thoroughly.
Mash the vegetables. Add the butter and mash until fairly smooth. Season with nutmeg, salt, and pepper to taste.