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. Meanwhile, saute onion in butter in a small skillet for 8-10 minutes or until golden brown.
Drain potatoes and carrots; mash. Beat in the onion, sour cream and salt. Sprinkle with chives.