Fill a steamer pot with 2 inches of water, add the steamer insert, and bring to a boil. Place the cauliflower florets in the steamer insert. Cover and steam for 15 minutes, until cauliflower can be easily pierced with a knife.
Place the steamed cauliflower into a food processor. Measure out 1/4 C of the steaming liquid, and pour into the food processor; purée until smooth. Add more liquid if necessary.
Add the butter, salt, and pepper into the food processor. Blend again. Taste and adjust seasoning if necessary. Serve hot. You can reheat over low heat in the same pan if you’re not eating immediately.