For the Turkey
Preheat the oven to 325°F. Remove giblets and thoroughly wash and dry the turkey.
Place turkey on a rack in a roasting pan. Mix the butter, thyme and oregano and then rub the herbed butter underneath and over the skin of the turkey. Pour the sherry and water into the bottom of the pan. Cover the turkey tightly with foil and put on the bottom rack of the oven for two hours.
Remove foil and continue roasting uncovered for about 1 more hour: until a meat thermometer (inserted into the thickest part of the turkey thigh) reads 175°F.
Remove the turkey from the oven and let rest on a cutting board (covered loosely with foil) for about 25 minutes before carving.
For the Stuffing
You can prepare the stuffing while the turkey is roasting. Combine the bread cubes with 2 cups of chicken stock, and the onion, celery, tarragon, sage, poultry seasoning and pepper. Place in a greased 9×13 baking dish. Increase the oven temperature to 350°F and bake the stuffing until it is heated through, about 30 minutes.
For the Gravy
After cooking the turkey, drain the juices from the roasting pan into a saucepan. Wisk 1 tablespoon of corn starch in a little bit of hot water and slowly add the cornstarch to the gravy. Continue stirring the gravy until it starts to thicken (you may need to add a bit more cornstarch).