Preheat oven to 400°F. Peel onions and cut each lengthwise in half, keeping root end intact. Combine remaining ingredients in a 12x8-inch baking dish. Place onion halves cut-side down in mixture.
Cover dish with foil. Bake 30 minutes, basting occasionally. Remove foil and cook 10 minutes longer or until onions are tender.
Makes 6 servings.