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 minutes until soft and golden. Let cool, then squeeze out the roasted cloves.
02 - Place potatoes in a large pot, cover with cold salted water, bring to a boil, then simmer for 15–20 minutes until fork-tender. Drain thoroughly.
03 - Return drained potatoes to the pot. Add roasted garlic cloves, softened butter, and warm milk. Mash until smooth and creamy.
04 - Stir in sour cream if using. Season with salt and pepper, adjusting texture with additional milk as needed.
05 - Transfer to a serving bowl, garnish with chopped chives or parsley, and serve hot.