Add 3 tablespoons of the reserved fat to the pan and heat until sizzling over medium-low heat. (If you do not have enough fat, make up the difference with melted butter.) Whisk the flour into the pan. Let the mixture bubble, whisking constantly, until it turns beige, about 1 minutes. Add the bourbon, then the broth mixture and whisk well. (This is your chance to eliminate any lumps, so put some elbow grease into it!) Bring it to a simmer, whisking up the browned bits on the bottom of the pan. Simmer, whisking occasionally, until the gravy has thickened and lost any taste of raw flour, 2 to 3 minutes. If the gravy seems too thin, increase the heat to medium and boil until it is as thick as you wish. If the gravy seems too thick, thin it with additional stock. Season to taste with salt and pepper. If desired, strain the gravy through a wire sieve to remove any extraneous bits of drippings. Serve it immediately. (Leftover gravy can be cooled, covered, and refrigerated for up to 3 days.)