Preheat oven to 400 degrees. Using a sharp knife, cut the tops off each head of garlic, about 1/4 inch down, which exposes the garlic cloves. Place the garlic heads onto a sheet of foil and drizzle with olive oil. Wrap and seal the foil at the top and roast for 45 minutes to an hour. The garlic should be tender, mellow, and lightly caramelized. Squeeze the cloves out and add to sauces, dressings, dips, softened butter, mashed potatoes, etc. Some people even spread roasted garlic directly onto toasted baguette slices.