Combine the giblet and neck from the turkey into a large saucepan with salt, onion, celery, and carrots.
Add water until the pan is ¾ full (about 5 cups).
Add bay leaf and simmer slowly while the turkey roasts in the oven. Add water as needed.
Before the turkey comes out of the oven, strain the giblet mixture, placing the solids (minus the neck bones) into a food processor and process until just slightly lumpy.
Add turkey drippings into broth from the giblets.
Combine cornstarch and ½ cup water. Add to broth mixture, stirring until smooth.
Cook over medium heat until thickened. Add back in the giblet meat, salt, and pepper. Serve warm.