Pour the turkey drippings into a bowl. Add a splash of chicken broth to the roasting pan and scrape up any browned bits; add to the bowl, then freeze the drippings until the fat hardens on top. (Alternatively, use a degreasing cup.) Spoon 1/2 cup of the fat into a saucepan. Add 1/2 cup flour; cook over medium heat, stirring, until golden, 4 minutes. Slowly whisk in 8 cups hot chicken broth; bring to a boil, then reduce to a simmer. Discard any remaining fat from the drippings; add the drippings to the saucepan. Simmer, whisking, until thick, 10 minutes. Season with salt and pepper. Strain to remove lumps, if needed.