I took the chicken fat from a roasted chicken and made gravy with it.  Make a roux with the fat, add a bit of butter if it looks scant and cook the raw out of a half cup of flour.  Stir cold stock into the hot roux and whisk away as it comes to a simmer.  Nothing better.  I bought a big cask of chicken powdered bouillon stuff so I add that in there for flavor and color.  I have to remind myself that the powdered stuff has a ton of salt so be careful but I never do in time.  Dummy.  Good thing the mashed potatoes need a lot of salt.