Collect drippings: After removing roast turkey from the pan, pour off all but 1/4–1/2 cup of fat from the roasting pan (add butter if needed to reach 1/4 cup total fat). Place the pan on the stovetop over medium heat.
Deglaze the pan: Pour 1–2 cups of warm stock into the pan. Use a wooden spoon or spatula to scrape up the browned bits (fond) from the bottom and sides. Simmer for 2–3 minutes to dissolve the fond completely. Strain through a fine-mesh sieve into a bowl, pressing on solids. Discard solids.
Make the roux: In a large saucepan, melt 1/4 cup of butter over medium heat. Sprinkle in flour and whisk constantly for 2–3 minutes until the mixture turns light golden (this cooks out the raw flour taste).
Whisk in stock: Gradually whisk in 4 cups of warm turkey stock (including the deglazed liquid), adding 1 cup at a time. Whisk vigorously after each addition to prevent lumps.
Simmer and thicken: Bring the mixture to a gentle simmer, continuing to whisk until it thickens (about 5–7 minutes). For thicker gravy, simmer longer or add a cornstarch slurry (2 tablespoons cornstarch mixed with 2 tablespoons cold water).
Season: Remove from heat. Season with salt, pepper, and Worcestershire or soy sauce if using. Add a sprig of thyme or sage for 5 minutes, then remove.
Strain and serve: Strain through a fine-mesh sieve into a gravy boat or serving bowl for smoothness. Serve immediately over turkey, mashed potatoes, or stuffing.