Melt the butter in a saucepan, over medium-low heat. Add the neck, giblets, onion, and cook stirring occasionally until browned, about 15 minutes. Add the broth, herbs, and bay leaf; cover and simmer over medium-low heat, about 2 hours. (This can be done while your turkey roasts.) Discard the giblets or reserve for chopping and adding to the gravy.

Pour all the turkey pan drippings into a liquid measuring cup or a degreasing cup. Set aside to let the fat separate from the darker pan juices. (Put the measuring cup in the freezer to helps them separate.)

Ladle off 1/2 cup of the fat from the top of the drippings, and transfer to a saucepan (or do it the old fashioned way in the turkey roasting pan.)

Heat the fat over medium heat. Scatter the flour evenly on top and cook, stirring constantly, with a wooden spoon until the flour browns slightly and smells toasty, about 4 minutes. Switch to a whisk; then gradually and carefully ladle the hot broth into the flour mixture while whisking constantly. Bring the gravy to a boil; adjust the heat so it simmers gently. Skim and discard any excess fat from the remaining drippings, and add the pan juices to the gravy. Continue to simmer, whisking occasionally, until the gravy is thickened, about 10 minutes. Chop and add giblets, if desired. Season with the Worcestershire, salt, and pepper.

Transfer gravy to a sauce boat and serve hot.