
In a large (10 to 12-inch), deep saute pan, cook the butter and onion over medium-low heat for 10 to 12 minutes, until the onions are lightly browned—don't shortcut this step as it gives the gravy phenomenal flavor.
Sprinkle the flour over the top, then stir in the salt and pepper. Cook, stirring continuously, for 1 full minute.
Gradually add the turkey drippings, whisking the entire time so that no lumps form.
Add the brandy and sage.
Bring to a simmer and let bubble gently, stirring often, until the gravy thickens to your liking, about 4 to 5 minutes. Carefully taste (it's hot!) and adjust seasoning as desired. Enjoy hot with everything.