01 - Preheat oven to 400°F. Place garlic cloves on foil, drizzle with olive oil, wrap tightly, and roast for 20 minutes until soft and golden.
02 - Place potatoes in a large pot, cover with cold water, add 1 tsp salt, bring to a boil, then simmer for 15–18 minutes until tender.
03 - Drain potatoes thoroughly and return them to the hot pot.
04 - Squeeze roasted garlic cloves from skins and mash with a fork.
05 - Add butter, roasted garlic, and sour cream to potatoes; mash until mostly smooth.
06 - Gradually stir in warmed milk until desired consistency is reached, then mix in Parmesan cheese.
07 - Season with salt and pepper to taste, transfer to a serving bowl, garnish with parsley if desired, and serve hot.