Pour enough olive oil into a baking pan (nonstick is best if you want more of the caramelized brown surface to stick to the garlic than to the pan) to make about a 1/16-inch layer. Lay garlic cut side down in pan, allowing about 1/2 inch around each piece. Set pan on rack in center or slightly above center of a 375¦ oven. Bake, uncovered, until garlic is browned on bottom and oozing at clove edges, 35 to 40 minutes. Now and then, lift edges of garlic with a spatula to check color. Rotate pan if browning is not even; keep in mind that few tastes are more bitter than burnt garlic-the smell will warn you of impending danger. As oil is absorbed, replenish it at least once with another 1/16-inch layer (generally, you use about 1 tablespoon oil for each head of garlic). Serve garlic hot, warm, or cool. If making ahead, cover when cool and let stand up to 1 day.