Double Cheddar Mashed Potatoes with Horseradish Recipe

Cook potatoes in large pot of boiling water until very tender, about 18 minutes. Drain in colander. Return potatoes to pot and mash with potato masher. Stir in butter and cheeses and mix until smooth. Add milk to make a creamy consistency. Stir in horseradish and half of the chives. Season to taste with salt and pepper. Place in serving bowl and sprinkle with additional cheese and remaining chives.