Remove the fully thawed turkey from the refrigerator and let it sit at room temperature for 45 minutes to 1 hour before roasting to promote even cooking.

Adjust oven racks so the turkey fits in the center with a few inches of clearance on top. Preheat oven to 325 degrees F.

In a medium bowl, stir together the fully softened butter, minced garlic, lemon zest, chopped thyme, chopped rosemary, salt, and black pepper until smooth and fully combined.

Place the turkey on a rimmed baking sheet. Remove from packaging and take out the neck and giblet bag from both the main cavity and the smaller neck cavity at the top.

Pat the entire turkey completely dry with paper towels inside and out. Season the inside of the cavity generously with kosher salt and black pepper.

Slide your fingers gently under the skin on each breast, loosening it carefully without tearing it.

Stuff the cavity loosely with the quartered onion, halved garlic head, quartered lemon, and fresh thyme and rosemary sprigs. Leave enough room for air to flow through.

Push a generous amount of herb butter under the loosened skin on each breast and press from the outside to spread evenly. Rub all remaining herb butter across every outside surface of the turkey.

Tuck the wing tips firmly underneath the body. Use kitchen twine to tie the legs together snugly close to the body.

Place the turkey breast side up on a rack set inside a large roasting pan.

Roast at 325 degrees F for 13 to 15 minutes per pound, or until an instant-read thermometer inserted into the thickest part of the breast and thigh reads 165 degrees F without touching bone. Cover loosely with foil if skin browns too quickly.

Remove from oven and let the turkey rest for 30 to 45 minutes covered loosely with foil before carving. Save all pan drippings for gravy.