2. Melt butter in a large pot over medium-high heat. Sprinkle in the flour; whisk constantly until the roux is golden brown.
3. Pour the gravy into the pot, whisking often. Bring to a boil, then reduce heat and simmer until gravy thickens.
4. At this point, I always whisk in some cornstarch to thicken the gravy further. In a small bowl, whisk together 1/4 c. water and 2-3 T. cornstartch. Add to the gravy and whisk constantly until gravy thickens. Remove from heat; gravy will thicken a little more. Keep warm until ready to serve.