How to Make It
Rinse the turkey inside and out under cold water and pat it thoroughly dry with paper towels. Season the cavity with 1 tablespoon of kosher salt and season the outside with 3 tablespoons of kosher salt. Cover and refrigerate the turkey overnight.
Remove the turkey from the refrigerator and pat dry with paper towels. In a bowl, blend the butter, sage and shallot and season with salt and pepper. Starting at the cavity end of the bird, slip your hand between the skin and meat, loosening the skin over the breast and around the legs. Spread the shallot-sage butter under the skin, covering as much of the breasts and legs as possible. Scatter the celery, carrots, onion and turkey neck in a large roasting pan and set the turkey on top; let stand at room temperature for 1 hour.
Preheat the oven to 375°. Spread the bread cubes on a large rimmed baking sheet and bake for 20 to 25 minutes, until golden. Let cool slightly, then transfer to a large bowl.
Increase the oven temperature to 425°. In a large skillet, heat the olive oil until shimmering. Add the celery and onion and cook over moderately high heat, stirring occasionally, until softened and barely browned, 7 minutes. Add the apples and giblets and cook, stirring occasionally, until the apples are just tender and the giblets are cooked, 5 minutes. Stir in the parsley, sage, thyme and rosemary and cook until fragrant, 1 minute. Add to the bread along with the chestnuts and the 2 cups of warm stock. Toss well and season the stuffing with salt and pepper; let cool.
Pack the turkey cavity and neck with the stuffing, then tie the legs together with kitchen twine. Roast for about 45 minutes, until richly browned. Baste with any accumulated pan juices and tent the breast with foil. Pour the remaining 2 cups of stock into the roasting pan. Turn the oven temperature down to 325° and roast the turkey for 2 to 2 1/2 hours longer, basting every 30 minutes; remove the foil for the last 30 minutes of roasting. The turkey is done when an instant-read thermometer inserted in an inner thigh registers 165°. Transfer the turkey to a carving board and let rest for at least 30 minutes.
Scoop the stuffing into a bowl. Strain the pan juices into a heatproof bowl and skim off the fat. Carve the turkey and serve with the stuffing and the strained pan juices.