Preheat oven to 350ºF.

Arrange the necks on a baking sheet. Drizzle with 2 tablespoons of olive oil and season with salt and pepper. Transfer to the oven and roast for 1½–2 hours until well-browned. Remove from the oven and set aside.

Place the necks and organs (heart, gizzard, or liver) you'd like in your gravy in a large pot. Place the onions, garlic, and rosemary on top. Cover with 6 cups of water and simmer for 2 hours.

Remove the necks and giblets and transfer them to a bowl. Turn the broth's heat to medium and rapid simmer for 15–20 minutes. You should be left with about 3 cups of broth.

Strain the broth through a fine mesh sieve into a bowl. Discard solids.

Once the giblets are cool enough to handle, pick the meat from the necks. Finely mince any of the organs you'd like in your gravy.

Melt the butter into a saucepan. Once frothy, add the flour. Cook for 1–2 minutes until nutty and aromatic.

Slowly whisk in 1 cup of the prepared broth to form a slurry. Continue whisking in the liquid in increments until the broth is incorporated and the sauce is smooth.

Add the 2 thyme sprigs and all of the neck and organ meat. Simmer over low heat for 10–15 minutes until thickened and bubbly. Season to taste with salt and white pepper. Turn off the heat and discard the thyme sprigs.

Serve warm with your favorite turkey dinner. Enjoy!