Put the roux back on low to medium heat. Slowly, in small amounts, add the chicken stock (or turkey juices), whisking the mixture vigorously until all the liquid has been absorbed in the roux. Continue to do this, in small drizzles, until the roux has expanded and liquefied into gravy. This will take awhile, perhaps ten minutes or so. When you have reached the consistency you desire for the gravy, add salt and pepper. Taste the gravy, and season according to your taste. Take it off the burner and serve.