In a small skillet, sauté onion in butter for 8-10 minutes or until golden brown.  Meanwhile, place potatoes and carrots in a large saucepan and cover with water.  Bring to a boil.  Reduce heat; cover and cook for 10-15 minutes or until tender.  Drain.

In a small mixing bowl, mash potatoes and carrots.  beat in onion, sour cream and salt.  Sprinkle with chives