1 1/2 lb Yukon Gold potatoes, peeled and cubed
1 1/2 lb swede (aka yellow turnip, rutabaga)
1 onion, thinly sliced
1/4 cup sour cream
1 tablespoon butter
1 tablespoon minced fresh rosemary
freshly ground black pepper
In a large pot, bring water to a full boil. Add potatoes, swede and onion. Cook until tender the potatoes and swede and easily pierced with a fork. Drain and return to pot. Add butter and sour cream. Mash.
I don't think Americans eat enough rutabaga (or as it is called elsewhere, swede. I don't know why not, it adds a peppery flavor to dishes and is a great way to add extra vegetables to things like soups or mashed potatoes without changing the texture.