As your turkey has thawed and has been rinsed you will find a small bag tucked up inside the cavity. Remove this small bag known as the giblets (the neck, heart, liver, and gizzard) from the inside of your turkey. Remove the giblets from the paper-ish bag they came in and discard the bag.
In a large saucepan over medium heat, saute the giblets with the onion and celery in butter, allowing them to cook until the giblets are browned and the butter has darkened slightly in color.
Add in chicken broth and bring the whole mixture to a boil. Reduce the heat to low and simmer the broth for 30 mins to one hour to deepen the flavor. After this step you can cover the pan and turn off the heat to let sit stovetop until the turkey is done cooking.
Once your turkey has finished cooking in the oven, remove the turkey from the oven and remove the turkey from the pan. Tent the turkey with foil and set aside. From the turkey roasting pan pour all the turkey juices into a pourable measuring cup. Let sit for several minutes for the fat to accumulate at the top of the juices. Spoon off the top fat from the turkey juices in that measuring cup and discard or save for use later in another recipe if you like.
ALSO, the next step is that you must scrape up all the browned flavor bits from the bottom of the turkey pan. Side note….the browned bits are flavor GOLD to add depth to your gravy-DON’T skip this part. Take the brown flavor bits/scrapings from the turkey pan and add them directly into the simmered saucepan.
Bring the pan of broth, turkey juices, and pan drippings to a boil again. For several minutes (about 10-20 minutes) let the saucepan simmer until the gravy is reduced by about one quarter. Then use a strainer to sift out all the giblet and vegetable solids. DIscard the giblets and return the smooth liquid to the pan.
Whisk in the glucomannan (about ¼ tsp per cup of liquid) and season to taste. The gravy will take a bit to thicken up so don’t overdo it. To start, add about ½ a teaspoon and add more glucomannen if your gravy isn’t thicker after 10 minutes.