In a large, heavy pot over medium heat, cook bacon until fat is rendered and bacon is beginning to brown.
Add rutabagas and pour in water to cover; bring to a boil; lower to a fast simmer; cook 25 minutes.
Add potatoes to the pot and cook until both vegetables are very tender; about 20 minutes more.
Drain, reserving about 2 cups of cooking liquid; set bacon aside.
Mash the vegetables together until smooth or, for a finer texture, put through a food mill.
Add reserved liquid, as needed, to loosen the mixture.
Finely mince bacon and add to the vegetables.
Add sugar, salt and pepper; stir well.
Taste and adjust the seasonings.
Transfer to a serving bowl and serve hot.
