Step 1Pulse together the salt, bay leaves, ground sage and black pepper in a spice grinder or mash them with a mortar and pestle to make a fine powder. Makes 1/3 cup. The mixture can be stored in a tightly sealed jar for up to 2 weeks.
Step 2Wash the turkey inside and out, pat it dry and weigh it. Measure 1 tablespoon of salt mixture into a bowl for every 5 pounds the turkey weighs (for a 15-pound turkey, you'd have 3 tablespoons of salt mixture).
Step 3Sprinkle the inside of the turkey lightly with the salt mixture. Place the turkey on its back and salt the breasts, concentrating the salt in the center, where the meat is thickest. You'll probably use a little more than a tablespoon. It should look liberally seasoned but not oversalted. Turn the turkey on one side and sprinkle the entire side with salt, concentrating on the thigh. Use a little less than a tablespoon. Flip the turkey over and do the same with the other side.
Step 4Place the turkey in a 2½-gallon sealable plastic bag, press out the air and seal tightly. Place the turkey breast-side up in the refrigerator. Chill for 3 days, leaving it in the bag but turning it and massaging the salt into the skin every day.
Step 5Remove the turkey from the bag. There should be no salt visible on the surface, and the skin should be moist but not wet. Wipe the turkey dry with a paper towel, place it breast-side up on a plate and refrigerate it uncovered for at least 8 hours.
Step 6On the day it is to be cooked, remove the turkey from the refrigerator and leave it at room temperature at least 1 hour. Heat the oven to 425 degrees.
Step 7Place the turkey on a roasting rack in a roasting pan; put it in the oven. After 30 minutes, reduce the oven temperature to 325 degrees, and roast until a thermometer inserted in the deepest part of the thigh, but not touching the bone, reads 165 degrees, about 2¾ hours total roasting.
Step 8Remove the turkey from the oven, transfer it to a warm platter or carving board; tent loosely with foil. Let stand at least 30 minutes to let the juices redistribute through the meat. Carve and serve.