To brine the turkey: Combine all of the ingredients for the brine in a large container. Add the turkey and let it brine in the refrigerator for 2 to 3 days.
To prepare the turkey for cooking: Remove the turkey from the brine the night before roasting and pat it thoroughly dry with paper towels. Combine the rosemary, sage, and butter for the herb crust in a small bowl. Season, to taste, with kosher salt. Work the butter under the skin of the turkey and massage it into the breasts and the legs. Massage the butter on the outside of the skin as well. Tie the legs together over the breast so they will protect it during cooking and help keep it moist and juicy.
Gravy preparation: Put the onions, carrots, celery, garlic, apples, bay leaves, cinnamon stick and thyme in a roasting pan and season with salt. Arrange the turkey on top of the veggies and refrigerate overnight UNCOVERED! Yes, that's right, uncovered. This will help the skin dry out and become really brown and crispy. Make sure that there is no raw food near the turkey in the refrigerator. After refrigerating overnight, the turkey is ready to go in the oven.
Preheat the oven to 450 degrees F.
Put 2 cups chicken stock and 1 cup apple cider in the bottom of the roasting pan. Roast the turkey in the preheated oven until the skin gets really nice and brown, about 40 minutes. Lower the oven heat to 350 degrees F for the remainder of the cooking time. Baste the turkey every 30 minutes or so and add more stock to the roasting pan, if needed. Cook about 17 minutes per pound. Once it gets to the proper color, tent the turkey with aluminum foil to prevent it from getting too dark.
Remove the turkey from the oven when an instant-read thermometer inserted in the thickest part of the turkey registers 160 degrees F. Make sure that the thermometer is not touching a bone when doing the reading. When the turkey has reached the proper temperature, remove it from the roasting pan to a cutting board and let it rest for at least 30 minutes. Cover loosely with aluminum foil.
Strain all the veggies over a bowl to separate them from the stock/mixture. Discard the veggies. Skim off the fat and add it to the roasting pan. This is the fat for the roux. Put the roasting pan over 2 burners and over a low heat and whisk in the flour. Cook until the mixture looks like wet sand, about 4 to 5 minutes. Slowly whisk in the remaining 1 cup apple cider, remaining chicken stock and the stock/cider mixture. Cook until the mixture has thickened and reached a gravy consistency. Taste and adjust the seasoning. Pour into a serving pitcher or bowl.
Carve the turkey, transfer to a serving platter and serve with the gravy.