01 - Set the oven to 400°F.
02 - Slice the top off the garlic bulb to expose cloves, drizzle with olive oil, wrap in aluminum foil, and roast for 30-35 minutes until soft and golden.
03 - Bring a large pot of salted water to a boil, add cauliflower florets, and cook for 10-12 minutes until very tender; drain thoroughly and let it sit to evaporate excess moisture.
04 - Squeeze the roasted garlic cloves from their skins.
05 - Combine cauliflower, roasted garlic, butter, milk, salt, and pepper in a food processor or mash by hand until smooth and creamy; adjust seasoning to taste.
06 - Transfer the mashed cauliflower to a serving bowl, garnish with chopped chives if desired, and serve warm.