Peel and cube the potatoes. Place the potatoes in a 3-quart saucepan; cover with water by 1 inch. Bring the water to a boil and reduce the heat. Simmer for 20 minutes or until fork tender. Drain.
Mash the potatoes with a hand masher or electric mixer. Stir in the sour cream and milk; beat with a spoon until creamy.
Stir in the remaining ingredients. Sprinkle with chili powder, if desired. Serve immediately.