How to Make It
Heat the oil in an enameled cast-iron casserole. Add the turkey parts and onion and cook over moderately high heat until lightly browned, about 5 minutes. Cover and cook over low heat until the turkey parts release their liquid, about 20 minutes. Add 4 cups of the water and bring to a boil. Cover partially and simmer over low heat until the broth is reduced to 3 cups, about 1 hour. Strain the broth into a medium saucepan and skim off the fat.
Pour the reserved turkey pan juices into a glass measuring cup and skim off the fat. Set the roasting pan over 2 burners on moderately high heat. Add the wine and boil for 2 minutes, scraping up the browned bits from the bottom of the pan. Scrape the contents of the pan into a strainer set over the turkey broth and press on the vegetables. Bring the broth to a boil. Mix the cornstarch with the remaining 1/2 cup of water until smooth, then whisk this slurry into the boiling broth. Reduce the heat to low and simmer until lightly thickened, about 2 minutes. Season with pepper, pour into a gravy boat and serve.