For the turkey: Preheat the oven to 375 degrees F.
Remove and reserve the heart and giblets from the turkey cavity; remove and discard the liver. Flip the turkey upside down so the breast is on your cutting board. Using kitchen shears, cut along both sides of the backbone to remove it. Using your fingers, gently separate the skin from the breast meat while keeping it attached. (You want to create a pocket for the sage butter without tearing the skin.)
Push the Sage Butter under the skin of the turkey, being careful not to puncture it. Rub the skin with olive oil, and sprinkle liberally with salt and pepper. Set aside.
For the gravy: Put the bay leaves, garlic, apples, celery, carrots, onions, cinnamon stick and thyme in a roasting pan and sprinkle with salt. Add 2 cups of the chicken stock and 1 cup of the apple cider, as well as the heart, giblets and backbone of the turkey.
Roast the turkey: Place a roasting rack on top of the vegetables and set the turkey on the rack. Roast for 1 hour 15 minutes. Tent the turkey with foil and continue roasting until an instant-read thermometer inserted into the leg (without touching bone) registers 175 degrees F. Let the turkey rest for 15 minutes before carving.
Meanwhile, finish the gravy: Strain all the veggies over a bowl; discard the veggies. Skim the fat from the pan juices and add it to the roasting pan; this is the fat for the roux.
Set the roasting pan over 2 burners over low heat and whisk in the flour. Cook until the mixture looks like wet sand, 4 to 5 minutes. Slowly whisk in the remaining 1 cup apple cider and 2 cups chicken stock, as well as the strained pan juices from the bowl. Cook until the mixture has thickened and reached a gravy consistency. Taste and adjust with additional salt and pepper as needed. Pour into a serving pitcher or bowl and serve with the turkey.
Mix the butter with the sage and some salt and pepper until well blended. Set aside.