Now it is time to make the roux. If you are using the separated fat, put it in pan and heat it up. You should have about a quarter cup of fat to which you will add a quarter cup of flour or cornstarch. If you have less than a quarter cup of fat, you can add some broth get to that amount. Just be sure to keep the roux ratio of 1:1 of fat to flour or cornstarch. When the fat is hot, add the flour or cornstarch. Stir until smooth. Slowly add your gravy mixture to the roux and heat it up. Allow the liquid to thicken to desired consistency. If it is too thick, add more broth. Add salt and pepper to taste.