Place garlic cloves in a small baking dish. Drizzle with olive oil, cover and roast 45 minutes, or until golden brown.
Bring a large pot of lightly salted water to boil. Add potatoes and cook until tender but firm. Drain and transfer to a large mixing bowl.
Place roasted garlic, milk, parmesan cheese and butter into the bowl with the potatoes. Season with salt and pepper. Mash with a potato masher or beat to desired consistency with an electric mixer - if you prefer.