Preheat your oven to 165°C (325°F). Ensure the oven rack is in the lower third of the oven. Remove the turkey from its packaging. Take out the giblets and neck from the cavities. Rinse the turkey inside and out with cold water and pat it thoroughly dry with paper towels. This step is crucial for achieving crispy skin.

Prepare the herb butter: In a medium bowl, combine the softened unsalted butter, finely chopped fresh rosemary, thyme, and sage, minced garlic, salt, and freshly ground black pepper. Mix well until all ingredients are evenly incorporated.

Gently loosen the skin over the turkey breast and thighs by carefully sliding your fingers between the skin and the meat. Be careful not to tear the skin. Evenly distribute about two-thirds of the herb butter mixture under the skin, pressing it gently to spread it over the breast meat and thighs. This will help keep the meat moist and flavorful during roasting.

Rub the remaining one-third of the herb butter all over the outside of the turkey skin. This will help the skin become golden brown and delicious.

Stuff the main cavity of the turkey with the quartered yellow onion, celery stalks, carrots, and the bunch of fresh parsley. These aromatics will infuse the turkey with wonderful fragrance as it roasts.

Truss the turkey: Tuck the wing tips under the body of the turkey. Tie the legs together with kitchen twine. Trussing helps the turkey cook more evenly and maintains a compact shape.

Place the prepared turkey on a rack in a large roasting pan. Pour the chicken or turkey broth into the bottom of the roasting pan. This broth will create steam, helping to keep the turkey moist, and will also form the base for your gravy.

Roast the turkey in the preheated oven. For a 5.5kg (12 lb) turkey, the initial roasting time is approximately 2.5 to 3 hours. A general guideline is about 20 minutes per pound (450g) at 165°C (325°F).

After about 1.5 to 2 hours of roasting, begin basting the turkey with the pan juices every 30 minutes. If the skin starts to brown too quickly, loosely tent the turkey with aluminum foil. This prevents burning while allowing it to cook through.

The turkey is done when a meat thermometer inserted into the thickest part of the thigh (without touching the bone) registers 74°C (165°F). The juices should also run clear when the thigh is pierced with a fork.

Once cooked, carefully remove the turkey from the oven. Transfer the turkey to a carving board and tent it loosely with aluminum foil. Let it rest for at least 20 to 30 minutes before carving. This resting period is crucial for allowing the juices to redistribute throughout the meat, resulting in a more tender and moist turkey.

While the turkey rests, you can make gravy from the pan drippings, if desired. Strain the pan drippings, skim off excess fat, and use them as a base for your favorite gravy recipe.