1Heat oven to 375ºF. Pierce potatoes with fork to allow steam to escape. Cut 1/4-inch slices from top of garlic bulb to expose cloves. Carefully remove most of the paperlike skin, leaving bulb intact and cloves unpeeled. Wrap garlic in aluminum foil. Bake potatoes and garlic about 1 hour or until potatoes are tender.
2Heat oil and oregano over medium heat 2 to 3 minutes or until oregano is fragrant; remove from heat.
3Open garlic packet to cool. Cut potatoes in half; carefully spoon potatoes into large bowl. Save skins for another use or discard. Separate garlic cloves and press the cloves slightly to squeeze garlic out into potatoes; discard skin. Add oil mixture and salt to potatoes.
4Mash potatoes until no lumps remain. Beat in milk in small amounts (amount of milk needed to make potatoes smooth and fluffy depends on kind of potatoes). Beat vigorously until potatoes are light and fluffy. Stir in chives.