Place beets and potatoes in a large pot with enough cold water to cover; salt water to taste. Bring to a boil and simmer until tender, 20 to 25 minutes.
Drain potatoes and beets and return to the pot. Shake them over medium heat to evaporate any remaining liquid. Pass through a ricer or mash. Stir in sour cream, butter, caraway seeds and season with salt and pepper.
