How to Make It
Place 3 quarts water, rutabagas, and 1 tablespoon of the salt in a large stockpot, and bring to a boil over high. Reduce heat to medium, and simmer until rutabagas are barely tender, about 10 minutes.
Meanwhile, heat cream in a small saucepan over medium, undisturbed, until steaming hot but not boiling. Remove from heat, and cover to keep warm.
Once rutabagas are tender, add potatoes to stockpot. Cook over medium until potatoes are tender, 20 to 25 minutes. Drain well, and return rutabagas and potatoes to stockpot. Add warm cream, butter, nutmeg, and remaining 2 1/2 teaspoons salt. Mash well until a few tiny lumps remain.
Transfer mixture to a serving bowl or platter, and sprinkle with parsley. Serve hot or warm with butter.