Preheat the oven to 425°F, with a rack in the lower-middle position.
Place the turkey breast-side down on a large cutting board. Using sharp poultry shears, cut along both sides of the backbone and remove it. Turn the turkey breast-side up and press firmly on the breastbone to flatten. Tuck the wing tips underneath. To save time, you can ask your butcher to spatchcock the turkey for you.
Pat the turkey thoroughly dry with paper towels.
Mix the mayonnaise, salt, garlic powder, paprika, poultry seasoning, and pepper. Spread an even coating over the turkey skin, including the breasts, legs, and thighs.
Place the turkey breast-side up on a large, sturdy rimmed sheet pan. Place a second, foil-lined sheet pan on the oven rack below to catch any drippings and prevent spills. Transfer to the oven with the legs toward the back.
Roast for 30 minutes, then reduce the oven temperature to 350°F. Continue roasting for 60 to 90 minutes, until the thickest part of the breast reaches 165°F and the thighs reach at least 165°F, ideally about 175°F for more tender dark meat, measuring away from bone. Begin checking after 75 minutes of total roasting time. Larger birds may take longer.
Transfer to a carving board and rest 30 minutes before carving.
To carve, remove the legs and separate the drumsticks from the thighs. Remove the wings. Cut along each side of the breastbone, following the rib cage to remove each breast half. Slice the breast meat crosswise and arrange on a platter with the legs and wings.
Notes
Salt Note: Use the full amount of Diamond Crystal kosher salt only for an unseasoned turkey. If using a kosher, self-basting, or salt-solution-enhanced turkey, reduce or omit the added salt.For a Larger Turkey: Increase the seasoned mayonnaise mixture proportionally based on the turkey's weight. Adjust the roasting time and use a meat thermometer to check for doneness.Nutrition Note: Nutrition is calculated using 6 ounces of skinless turkey breast. Values will vary depending on the cut and whether you eat the skin.