Place the garlic heads in a baking pan, cut side up. (A muffin pan works great for this, as it keeps the garlic bulbs from rolling around.) Drizzle a couple teaspoons of olive oil over each exposed head, using your fingers to rub the olive oil over all the cut, exposed garlic cloves. Cover the bulb with aluminum foil. Bake at 400°F for 30-35 minutes, or until the cloves feel soft when pressed.