Peel garlic cloves, toss with olive oil, wrap in foil, and roast at 350 degrees F for about 30 minutes, or until softened. Meanwhile, bring the water to a boil and add the potatoes and salt. Simmer until potatoes are cooked, about 10 minutes. Drain. Mash the potatoes with the cream, mashed roasted garlic, and pepper. Stir in butter, and serve.