Place the turkey neck, heart, and gizzard in a medium saucepan. Add the onion, carrot, celery, bay leaf, and peppercorns.

Pour in the 4-5 cups of water or broth, ensuring everything is covered.

Bring to a boil, then reduce the heat to low, cover, and simmer gently for 1 to 1.5 hours. The meat should be very tender.

While the stock simmers, prepare the liver if using. Sauté the turkey liver in 1 tsp of butter for 2-3 minutes per side until just cooked through. Finely chop it and set it aside.

Once the stock is done, use a slotted spoon to remove the neck, heart, and gizzard. Strain the stock through a fine-mesh sieve into a bowl; discard the vegetables. You should have about 3-4 cups of rich stock.

When the cooked giblet meats are cool enough to handle, pick all the meat off the neck and finely chop it along with the heart and gizzard. Set this chopped meat aside.

Pour all the drippings from your turkey roasting pan into a large liquid measuring cup or a fat separator.

Let it stand for 5-10 minutes. The fat will rise to the top. Skim off 1/4 cup of this clear yellow fat and set it aside. This is your "liquid gold" for the roux.

The remaining dark, savory drippings (the "jus") will be used for the gravy.

Place the large skillet or roasting pan (that you cooked the turkey in, if you like) over medium heat.

Add the 1/4 cup of reserved turkey fat (or use butter if you didn't have enough fat).

Sprinkle the 1/4 cup of flour over the fat and immediately start whisking.

Cook the roux, whisking constantly, for 3-5 minutes. It will bubble and then smooth out. You want it to turn a light peanut butter color and smell nutty.

My Hard-Won Tip: Do not rush this step. Cooking the flour for at least 3 minutes gets rid of that "raw flour" taste. I've made this gravy over 20 times, and this is the non-negotiable step for a professional-tasting gravy. A darker roux means a darker, more complex gravy.

Slowly—very slowly at first—pour about 1 cup of the warm giblet stock into the roux, whisking vigorously. The mixture will seize up and look like a thick paste. This is normal!

Keep whisking and gradually pour in the rest of the giblet stock and all the reserved turkey drippings (the jus, not the fat).

Bring the gravy to a simmer, whisking often, until it thickens enough to coat the back of a spoon (about 5-10 minutes).

Stir in the reserved chopped giblet meat and the optional chopped liver.

Taste the gravy. This is the most important part. Add salt and pepper as needed. Roasting drippings vary wildly in saltiness, so always taste before you season.

For a silky, restaurant-quality finish, turn the heat to low and whisk in 1-2 tablespoons of cold butter until it melts. This is a classic technique called monter au beurre.

Stir in the fresh herbs (if using) just before serving.