Place garlic on a square of aluminum foil; drizzle with oil and wrap in foil.
Bake at 425° for 30 minutes; remove from oven and set aside.
Cook potatoes in boiling water to cover, 15 to 20 minutes or until tender; drain and transfer to a large mixing bowl.
Add butter and next 3 ingredients; beat at medium speed with an electric mixer until fluffy.
Cut off pointed ends of garlic; squeeze pulp from garlic cloves and stir into mashed potato mixture.