Night before prep. This step is optional but does help in making a tender turkey with crispy skin. The night before cooking, remove the turkey from the packaging, pat dry all over, and season generously with salt. Wrap with saran wrap, place in a roasting pan in the fridge overnight.
Prep the foil. Take the turkey out of the fridge 2 hours before cooking and let it sit at room temperature. Unwrap the turkey and pat dry. Take a large enough piece of aluminum foil to fit over the breast and wings of the turkey. Mold it to fit over the breast, shiny side up. Remove, spray the not shiny side with cooking spray, and set aside.
Make the herb butter. On the day of cooking, make the herb butter. Remove the thyme leaves from the springs and cut the stems off the parsley. Pulse in a food processor until chopped. Add the butter and blend on low until combined.
Prep the turkey. Preheat the oven 450°F and transfer the rack to the lowest setting. Season the turkey with salt and pepper all over. Using clean hands (or you can wear gloves) separate the skin from the breast of the turkey, going slow so as not to break the skin. You just want a small enough space to fit your hand. Rub about 2 tablespoons under the skin on both sides of the breast of the turkey. Rub the remaining herb butter into the breast skin and on top of the legs and wings.
Stuff the turkey. Inside the cavity of the turkey, add the celery, carrots, a small bunch of parsley and thyme sprigs, half the garlic, half the onion, and two quarters of the lemon. Tie the leg bones together.
Prep the pan liquid. Add the remaining onion, garlic, and lemon to the bottom of the roasting pan with the reserved organ meat and neck. Pour the apple cider and turkey stock into the roasting pan. The total amount of liquid you need will vary depending on the size of your turkey since the roasting times are different and the liquid will reduce as it cooks. A smaller turkey will need 1 to 1 ½ quarts, where a large turkey will need 2 quarts.
Cook the turkey. Place the rack in the roasting pan and the turkey on the rack breast side up. Cook the turkey for 40 minutes at 450°F. Reduce the heat to 350°F and place the greased foil over the breast. Cook for 11 minutes per pound, about 2 to 4 hours depending on the size of your turkey. The thickest part of the breast should read 161°F and the thigh 181°F, the turkey will continue to cook as it rests.
Rest and slice. Transfer the turkey to a cutting board and cover completely with foil. Let rest 20 to 30 minutes before carving, which will give you time to reheat and/or finish side dishes and gravy.
Make the pan gravy. Strain 2 cups of the pan drippings into a saucepan, skim the fat from the gravy using a turkey baster or slices of bread - just lay the bread on top of the drippings for about 10 seconds, flip and repeat until the bread starts to soak up the drippings. Remove about ½ cup drippings to a bowl. Whisk in the flour until it makes a clump-free paste. Slowly add more drippings or stock until it becomes a smooth slurry. Add the slurry to the saucepan and whisk in 2 cups chicken or turkey stock. Bring to a slow boil over medium-high heat, whisking occasionally. Once the gravy is thickened and bubbling, turn off the heat and transfer to a serving dish.