Boil the chopped rutabaga until tender: In a large pot, cover the chopped rutabaga with about 1 inch of cold water. Add a generous pinch of salt and boil until tender, about 30 to 40 minutes. Drain and return the rutabagas to the pot.

Steam, then mash: Reduce the heat to low and let the rutabaga steam for a minute or two. Then, mash with a potato masher.

Add the butter and sour cream, then season to taste: Just before serving, mix in the chopped dill.