1) Melt butter or meat drippings on medium-low heat.
2) Add equal parts flour to the amount of butter/fat. Whisk until combined. This will form a golden paste which is your roux.
3) Cook over medium-low heat until roux mixture is golden brown. This really brings out the flavor of the roux.
4) Add in liquid ingredients (i.e. milk, cream, or broth). Whisk mixture until all flour lumps are gone. Bring mixture to boil to thicken. Season with salt and pepper to taste.