Transfer drippings to a medium saucepan. Add 3 ½ cups of the chicken broth.
Bring to a boil over high heat. Reduce heat to low, and simmer for 20 minutes.
Whisk together ¼ cup all-purpose flour and the remaining ½ cup chicken broth in a small bowl; whisk into broth mixture.
Bring to a boil over high; reduce heat to medium and boil gently for about 20 minutes, until gravy has reduced and thickened. Serve with roasted turkey.