Preheat the oven (with one of its racks positioned in the bottom third) to 425°F.
Use paper towels to pat the turkey dry, inside and out, then place the bird breast-side up on a roasting pan fitted with a rack. In a small bowl, stir together the oil, salt, and black pepper, then rub the mixture all over the turkey’s skin. Transfer to the fridge and chill, uncovered, at least 8 and up to 24 hours.
Right before you plan to cook the turkey, make the stuffing: In a medium pot over medium-high heat, melt 10 tablespoons of the butter. When the foam begins to subside, add the onions and celery and cook, stirring occasionally, until softened, 8–10 minutes. Add the mushrooms and celery root and continue cooking until the mushrooms release their liquid and soften, 12–15 minutes. Stir in 1½ cups of the stock, and the parsley and sage. Season to taste with salt and black pepper, then bring to a boil. Remove from the heat, stir in the bread, then set aside until cool slightly.
Once the stuffing is cool enough to handle, place half of the mixture inside the turkey. Transfer the remaining stuffing to a 9- by 13-inch baking dish, dot with 3 tablespoons of the butter, and set aside.
Melt the remaining 11 tablespoons of butter, then brush it all over the turkey. Pour the remaining stock into the roasting pan, then transfer to the oven and roast until the skin begins to tighten, about 15 minutes. Turn the heat down to 350°F and continue cooking, basting the turkey every 30 minutes, until an instant-read thermometer inserted into the thighs reads 165°F, about 3 hours.
Remove the turkey from the oven, then use tongs or two heavy forks to transfer the bird to a large cutting board. Set aside to rest at room temperature for 15–30 minutes before carving.
Meanwhile, transfer the baking dish of stuffing to the hot oven and bake until golden brown, 20–30 minutes.
Meanwhile, make the gravy: Pour the pan drippings into a medium bowl and set aside. Place the roasting pan directly on the stove top over medium heat. When the pan begins to sizzle, add wine and cook, using a wooden spoon to scrape up any browned bits from the bottom of the pan, until reduced by half, about 4 minutes. Add stock; bring the liquid back to a boil, then transfer to a heatproof bowl and set aside.
In a large skillet over medium-high heat, melt the butter. When the foam begins to subside, add mushrooms and shallots and cook, stirring occasionally, until soft and golden, 15–20 minutes. Sprinkle over the flour, stir to combine, then stir in the reserved pan drippings. Bring to a full boil, cook for one minute, then lower the heat to simmer and cook until the gravy hsa thickened, about 8 minutes. Stir in any reserved chopped giblets from making the turkey stock (if using), along with the cream and lemon juice. Season to taste with salt and pepper and remove from the heat.
To serve, carve the turkey and serve hot, with the stuffing and gravy on the side.