Separate the cauliflower into florets and discard the core.
Bring about 2 cups of water to a simmer in a pot, then add the cauliflower. Cover and turn the heat to medium. Cook the cauliflower for 12-15 minutes or until very tender.
Drain and discard all of the water (the drier the cauliflower is, the better) and add the milk, butter, sour cream, salt and pepper and mash with a masher until it looks like “mashed potatoes.” Top with chives.