Prepare your smoker or grill for two-zone cooking by placing preheated charcoal briquettes on one side of the grill to create a hot and a cool zone. Close the bottom vents almost entirely for low heat cooking (225-250 degrees) and add 2-3 chunks of your favorite smoking wood to the preheated charcoal briquettes; this will give the gravy a deep smoky flavor.
Place turkey stock or turkey broth to a disposable aluminum half pan and place the pan on the grill’s main cooking grate. Cover the grill and allow the broth or stock to absorb the smoke flavor for approximately 45 minutes until the preferred level of smokiness has been achieved. Remove the pan from the grill and set it aside. Open the bottom vents slightly to increase the temperature to approximately 350 degrees.
Place a small saucepot on the hot portion of the grill and add the butter and flour. Stir the flour and butter mixture continuously for approximately 10 minutes until the roux begins to turn golden brown (you can continue to cook and stir the roux if you wish to have a darker, richer flavor).
When the roux browns, pour the turkey stock and drippings from the aluminum pan in to a fat separator (alternatively you can use a spoon to remove as much of the fat as possible from the top of the liquid). Slowly add the separated liquid to the roux while stirring continuously to remove any possible lumps.
Let the gravy simmer until warmed through then serve alongside your holiday roast.