Remove the turkey from its package, making sure to remove the neck and giblets from the cavity. Place on large cutting board and pat completely dry with a few paper towels.
Flip the turkey over so the breast side is down. Using large poultry shears or a very sharp large knife, cut through the bones on either side of the spine. Discard the spine or use in stock for gravy. Flip the turkey over and lay it flat so the breast side is up. Place the palms of your hands directly on top of the turkey in the center and then firmly press down on the breast bone to flatten out the turkey as much as possible. You might hear a few cracks.
Place a wire rack over a large and sturdy baking sheet. Then transfer the turkey onto the rack laying it flat, breast side up.
Use your fingers to loosen the skin from the breast and the thighs, creating pockets. Sprinkle salt in those pockets and all throughout the underside of the turkey and finally on top of the skin as well. Stuff the thyme and rosemary under the skin of the breasts and the thighs. Cover loosely with plastic wrap and chill in the fridge for 24 hours or up to 36 hours.
Preheat oven to 425°F.
Remove the turkey from the fridge for 1 hour before cooking. Place bits of the softened butter underneath the skin of the breasts and thighs and then rub the remaining butter all over the top of the turkey. Sprinkle with black pepper. Roast in the oven until golden and crispy and the internal temperature reaches 150°F. It’ll continue to cook to 165°F when you remove it from the oven and let it rest. Rotate the pan halfway through cooking for even browness.
Remove the turkey from the oven, transfer to a large cutting board and let rest for 30 minutes before carving. This will ensure that the juices redistribute and don’t just leak out. Carve and serve.