Pat the spatchcocked turkey very dry with paper towels. In a small bowl, mix the kosher salt, baking powder, and black pepper. In another bowl, combine the softened butter, olive oil, minced garlic, thyme, rosemary, sage, lemon zest, and orange zest.

Gently loosen the skin over the breasts and thighs with your fingers. Rub about half the herb butter under the skin directly onto the meat, and spread the remaining butter all over the skin and underside of the turkey.

Place the turkey skin side up on the rack or vegetables, tucking the wing tips behind the breasts. Pour 1 cup stock into the pan, avoiding the skin, to start flavorful drippings and reduce smoking.

Roast at 450°F (232°C) for 20 minutes to begin browning. Reduce the oven temperature to 375°F (190°C) and continue roasting, rotating the pan once for even cooking. Start checking the internal temperature early. The turkey is ready when the thickest part of the breast and the innermost part of the thigh both reach at least 165°F (74°C). Cooking time will vary depending on the turkey's size and your oven.

If the skin darkens too quickly, tent the darkest areas with small pieces of foil. Add a splash more stock to the pan if it dries out or begins to scorch.

Transfer the turkey to a carving board and rest for 20 to 30 minutes. Meanwhile, skim excess fat from the pan drippings, mash the roasted garlic into the juices, and reduce briefly on the stovetop for spooning, if desired.

Carve by removing the legs and thighs, then slice the breast meat across the grain. Arrange on a warm platter, spoon with some pan juices, garnish with fresh herbs, and serve hot.