Place the cauliflower and garlic in the microwave steamer and cook on high for 8 minutes, or until cauliflower is fork tender. Drain the water from the steamer and let cauliflower cool for 10 minutes before proceeding.
Transfer the cooked cauliflower and garlic to a food processor bowl. Add the butter, 2 tablespoon chopped chives, salt, and pepper to the steamed cauliflower and process for 30 seconds.
Gradually pour the heavy cream into the food processor while continuing to process for 1 minute, until the cauliflower puree is smooth and creamy.
Transfer the mashed cauliflower to a large bowl for serving. Top with the remaining butter and sprinkle with the remaining chives.