* I use dairy-free, soy-free margarine and it works just fine. If you can handle butter, by all means use butter. You can also use lard, if you aren't worried about the fat content. Some people use meat drippings, but sometimes there is liquid other than fat mixed in, and I find it messes with the balance of my "roux."
** In the gravy pictured above, I used brown rice flour. I have also used a gluten-free all-purpose flour mix before. I imagine any flour you have on hand could work just fine.
Melt butter/margarine ("fats) in a small saucepan over low heat. Whisk in the flour until you form a roux.
Continue to cook the roux, whisking constantly, until it starts to turn golden brown. This will cook the flour so that its taste isn't noticeable in the final dish.
Gradually whisk in the stock. Bring to a boil over medium heat, stirring constantly.
Add sage leaves, then boil, still stirring, for one minute. Remove from heat. Add salt and pepper, and serve.