For the dry brine, rub the entire bird (inside and outside the cavity) with the sea salt. Place in a large bowl, to collect any drippings, cover, and refrigerate for 24 to 48 hours. Once finished, rinse the duck completely and pat dry.
Turn oven to 300 F.
Prick the skin of the duck with a sharp knife all over, focusing especially on the skin over the thick breast tissue.
Rub the duck with the salt and pepper, place on a roasting pan, cover with foil, and bake at 300 F for 1 1/2 hours.
Turn oven up to 400 F. Uncover the duck and bake for an additional 30 minutes, or until the internal temperature reaches 165 F in the thickest part of the breast.
For the plum sauce, place all the ingredients in a medium-sized sauce pot over medium heat. Cover and let simmer for 10 to 15 minutes, or until most of the plums have broken down. Stir to continue breaking down the plums and then set aside off heat until serving. Note: if it looks dry, feel free to add a splash of water until it's at a consistency you like.
Once the duck is finished cooking, let it rest for 10 to 15 minutes then carve for serving.
To retrieve the duck fat, use a spoon or baster to siphon the duck fat into a storage container. Store the fat in the refrigerator for future use!
Serve with chopped chives (if you desire) and the plum sauce.
Enjoy!