Combine salt & spices. Rub the turkey with oil, then season liberally with spice mix over the skin and underneath the skin of the breasts.
Arrange turkey on a roasting pan or sheet pan, loosely tent with plastic and refrigerate overnight, up to 2 days.
To prepare clarified butter, simmer butter in a saucepan until melted. Skim the white foam off the top. When frothing subsides, pour butter through cheesecloth. Clarified butter is better suited to use for roasting at high temperatures without burning!
Remove the brined turkey from the fridge. Scatter the onion, carrot, and celery over the bottom of a large roasting pan. Pour in enough water or stock to cover the bottom of the pan. Lay the turkey over the vegetables, or elevated on a cooking rack set in the pan. Tuck wing tips underneath the breasts or wrap with foil. Brush turkey with clarified butter, also smearing some underneath the skin of the breasts.
Preheat oven to 450°F. Insert a probe thermometer into the thickest part of the breast to monitor temperature. Once the oven is ready, place the turkey on the middle rack.
Cook for 15 minutes, then reduce the oven temperature to 350°F. Roast until the internal temperature of the breasts reads 155°F and the thighs are at least 170°F.
Remove turkey from the oven and allow to rest for at least 15 minutes before carving. Roasted drippings can be strained and added to gravy.