Put the rutabaga in a large saucepan and cover by about 2 inches of water. Season the water generously with salt.
Partially cover the pot and bring the water to a boil over medium-high heat. Boil the rutabaga for 40 minutes; rutabagas take a long time to bring out their natural sweetness. Add the potatoes to the pot and cook until the potatoes are fork tender, about 15 minutes.
Heat the cream in a small saucepan over medium heat.
Drain the rutabagas and potatoes from the water and pass through a food mill. Add half the hot cream and cold butter into the milled rutabaga/potato mixture and stir vigorously to combine. Repeat this with the remaining cream and butter. Taste to make sure the seasoning is correct.
Recipe courtesy Anne Burrell
Recipe courtesy of Rachael Ray