Preheat oven to 425 (or less, maybe 400). Pell the outermost skins off the garlic heads. (Note: I don't always do that. --mrm) Cut top 1/4th off. This step is crucial! Place the heads in a small roasting dish and drizzle with olive oil. Add herb sprigs. Cover tightly and roast for 30-45 minutes, until bulbs are soft and golden colored. You can test them after 30 or 35 minutes by squeezing on a head, and seeing if it gives. You do want the cloves to be soft.
Let cool. When cool enough to handle, press bulbs out of skins. Or, alternatively, place entire heads on dinner table and invite guests to squeeze out the garlic that they want, onto bread.
This goes great with Italian breads or with dark German breads like rye.