On a large cutting board, using a sharp chef’s knife or a cleaver, hold the turkey upright with the breasts facing away from you and cut through the left side of the back down to the tail.
While holding the spine, cut down the right side of the spine and remove it. Lay the turkey breast-side down on the cutting board.
Using sharp kitchen shears, cut away the ribs located just below the wings. Cut between the skin and the flesh and through the bottom of the ribs, horizontal to the cutting board. Removing the ribs helps the bird lay flat in the pan.
Flip the turkey over and, using your body weight, press down on the breastplate, located right between the breasts, until it cracks and the turkey lies flat. If you have trouble cracking it, cover the turkey with a sheet of plastic wrap or a clean towel and pound the breastplate with a heavy rolling pin.
Once flat, tuck the wings behind the breasts, pull the thighs up and over the breasts and tie the legs together with baker’s twine.
Transfer the turkey to a roasting pan with a rack that has been sprayed with non-stick spray. The rack allows hot air to flow under the turkey, evenly cooking the underside.
Season both sides generously with salt and pepper.
Gently pull the breast skin away from the meat, being careful not to tear the skin, and push the butter between the skin and the breasts as far as your fingers will allow. Replace the skin over the breasts if necessary.
Cover turkey with plastic wrap and let sit at room temperature for one hour.
Position the oven rack to the second-lowest level and preheat the oven to 450° F. Insert the oven-safe probe or meat thermometer into the thickest part of the breast, making sure that the end of the probe is not touching bone (the reading will be inaccurate).
Using a measuring cup filled with water, fill the roasting pan with approximately an inch of water to prevent dripping turkey fat from burning on the bottom of the pan.
Place the turkey in the oven and roast for approximately 90 minutes, rotating after 40 minutes, or until the internal temperature of the breast reads 165° F.
Remove the turkey from the oven and loosely cover with foil for 20 minutes prior to carving.