01 - Preheat the oven to 400°F.
02 - Slice off the top quarter of the garlic head to expose the cloves. Drizzle with olive oil, wrap in foil, and roast for 35 to 40 minutes until soft and golden. Let cool slightly, then squeeze out the roasted garlic cloves.
03 - Place potatoes in a large pot and cover with cold salted water. Bring to a boil, then reduce to a simmer and cook for 15 to 20 minutes until fork-tender. Drain thoroughly.
04 - Return potatoes to the pot. Add roasted garlic, butter, warm milk, and cream. Mash until smooth and creamy.
05 - Season generously with salt and freshly ground black pepper. Adjust the consistency with additional warm milk if desired.
06 - Transfer to a serving bowl and garnish with chopped chives or parsley if using. Serve immediately while hot.