Measure and return quarter cup to pan. Sprinkle flour into fat; cook and stir 2 or 3 minutes over low heat. Add water and 2 cups of the reserved turkey stock. Cook, stirring and scraping up browned bits in pan with wooden spoon, until gravy thickens and bubbles 2 minutes. Strain gravy into saucepan; add chopped giblets and reserved liver. Taste; season with salt and pepper if needed.