Take the turkey out of the fridge. Rub the Cajun herb butter all over the turkey, including under the skin (especially over the breast).
Fold the wings back under the turkey to prevent them from burning, but do not truss the legs.
Place the turkey on top of the mirepoix in the roasting pan.
Pour 2-3 cups of stock into the bottom of the pan.
Transfer to the oven and roast for approximately 2 ½ to 3 ½ hours, or until the thickest part of the breast registers 155°F to 160°F on a meat thermometer.
Every 30-45 minutes, baste the turkey with the juices and melted butter in the bottom of the pan. If needed, add more stock to the pan.
Once it reaches the desired temperature, remove the turkey from the oven and tent it loosely with foil. Let it rest for 20-30 minutes before carving.
You can use the pan drippings along with the mirepoix to create a flavorful gravy. Strain the liquid and simmer it in a pot, adjusting seasonings as necessary.