Prepare the stock: Melt 2 tablespoons butter in a large saucepan over medium heat. Add the turkey neck and giblets; cook, turning, until browned, about 5 minutes. Add the onion, carrot, celery, herb sprigs and bay leaves; stir to coat. Add the wine and bring to a boil, scraping up any browned bits from the bottom of the pan. Cook until reduced by half, 2 to 3 minutes. Add the broth, reduce the heat to low and simmer about 1 hour. Strain through a fine-mesh sieve into a large measuring cup; reserve the saucepan. You should have 7 cups stock ¿ if you're short, add more broth.
Melt the remaining 8 tablespoons butter in the reserved saucepan over medium heat. Add the flour and whisk until smooth and bubbling, about 2 minutes. Gradually whisk in the 7 cups stock; bring to a simmer and cook, whisking occasionally, until thickened, about 10 minutes. Set aside until the turkey is done.
Pour the turkey pan drippings into a fat separator and let stand until the fat rises to the top. Discard the fat (or drizzle on your stuffing). Whisk the defatted drippings into the gravy; season with salt and pepper. Simmer until desired thickness, 5 to 15 minutes.