Preheat your oven to 425 degrees Fahrenheit. Place parchment paper on a rimmed baking sheet and set aside.
Remove the neck and giblets from the thawed turkey. Place the turkey breast side down on a cutting board. Locate the backbone. It is easiest to find by looking for the small piece of tailbone that sticks out of the bottom of the bird. Use very sharp kitchen shears to cut on one side of the backbone all the way to the top of the turkey. Then repeat on the other side to fully remove the backbone. (See photos in the post.)
15 pounds thawed turkey
Turn the turkey over, spreading the turkey out flat. Press down so it lays fully flat. You may hear a pop – this is the breastbone breaking. Place the turkey on the prepared baking sheet.
In a small bowl combine the butter, rosemary, salt, black pepper, garlic powder, onion powder, thyme, and sage. Gently spread the mixture under the skin of the turkey, working to cover the breasts and thighs evenly.
12 tablespoons unsalted butter, 3 tablespoons dried rosemary, 1 tablespoon kosher salt, 1/2 tablespoon black pepper, 1 1/2 teaspoons garlic powder, 1 1/2 teaspoons onion powder, 3/4 teaspoon dried thyme, 3/4 teaspoon dried sage
Coat the outside of the turkey with olive oil. Then season with salt and pepper.
2 tablespoons olive oil, 1 teaspoon kosher salt, 1/4 teaspoon black pepper
Bake the turkey for 70 to 90 minutes or until a thermometer inserted in the thickest part of the turkey breast registers 165 degrees Fahrenheit. You may need to cover the turkey with foil after about 45 minutes of cooking to prevent it from browning too much. Allow the turkey to rest for 10 minutes before slicing and serving. This will prevent the juices from running out of the meat when you cut into it, keeping your turkey moist and delicious.