Once you've roasted your turkey, pour any pan drippings into a degreasing cup or small bowl. Reserve 2 tablespoons of the fat, discarding the rest, and add the separated juices to the broth. Add the reserved fat to the roasting pan and place on a burner over medium-high heat. Add the shallot, garlic, rosemary, thyme, and bay leaf; season with salt and pepper. Cook until shallot is tender, about 3 minutes.
Meanwhile, make a paste with the butter and flour in a small bowl; set aside. Add the broth and scrape up any browned bits from the bottom of the pan with a wooden spoon. Bring to a boil and whisk in the flour mixture. Boil until sauce thickens to make a gravy, about 4 to 5 minutes. Adjust seasoning, to taste. Remove and discard the garlic and bay leaf. Serve.