Season Whole Duck (1) inside and outside with Kosher Salt (to taste).
Preheat your oven to 400 degrees F (200 degrees C).
Place on a rack over a rimmed tray, to catch the fat and juices. Place into a 400 degrees F (200 degrees C) degree oven, turn down temperature to 300 degrees F (150 degrees C), roast for 3 Hours and 45 Minutes, turning every 30 Minutes.
After 3 Hours and 45 Minutes, turn the temperature to 425 degrees F (220 degrees C) remove the duck with the rack, and place it on another tray (I used a cast iron pan). Roast breast-side up for another 20 to 30 minutes or until the skin is very crisp and golden brown.
Remove from oven and let rest for 10 minutes before carving.
Add Red Wine (2 cup) to the bottom tray used to roast the duck. Simmer until all the fond has loosened from the bottom of the tray.
Add Demi-Glace (1 cup), simmer another minute.
Strain the sauce, check and adjust the seasonings.
Because of its large size, carve what you will serve to eat and store the rest for another day. Serve with the red wine jus and choice of sides.