Place potatoes in a Dutch oven; add water to cover. Bring to a boil. Reduce heat; cook, uncovered, until tender, 15-20 minutes. Meanwhile, place oil and garlic in a small food processor; process until blended. , Drain potatoes; return to pan. Mash potatoes, gradually adding cream, butter, salt, pepper and enough milk to reach desired consistency. Stir in green onions. Serve with garlic-olive oil and, if desired, cheese.