Heat oven to 450 degrees F.
Put turkey on a cutting board breast side down and cut out backbone. Turn turkey over, and press on it to flatten. Put it, breast side up, in a large roasting pan. Wings should partly cover breasts, and legs should protrude a bit.
Tuck garlic, thyme and rosemary under the bird and in the nooks of the wings and legs. Drizzle with olive oil, and sprinkle liberally with salt and pepper.
Roast for 20 minutes. Turkey should getting brown. Remove from oven, baste with pan juices, and return to oven. Reduce heat to 400 degrees (if turkey browns too quickly, reduce temperature to 350 degrees).
Begin to check turkey's temperature about 15 minutes later (10 minutes if bird is on the small side). It is done when thigh meat registers 165 degrees on an instant-read meat thermometer. Check it in multiple places. Let turkey rest for a few minutes before carving, then serve with garlic cloves and just the pan juices to pan a gravy