01 - Preheat oven to 400°F. Slice off the top of the garlic head, drizzle with olive oil, wrap in foil, and roast for 30 to 35 minutes until soft. Let cool, then squeeze out the cloves.
02 - Place potatoes in a large pot, cover with cold water, add 1 teaspoon salt, bring to a boil, then simmer for 15 to 20 minutes until fork-tender. Drain thoroughly.
03 - Return potatoes to the pot. Add roasted garlic cloves, butter, and sour cream. Mash until smooth and creamy.
04 - Gradually stir in warm milk until the desired consistency is reached. Season with the remaining salt and black pepper.
05 - Transfer mashed potatoes to a serving bowl and sprinkle with chopped chives if desired. Serve hot.