Step 1Bring a pot of water to the boil.
Step 2While the water is heating, place the duck on a cutting board, breast-side up and with the legs facing you. Remove any large pockets of fat around the cavity, then gently but firmly begin loosening the skin from the meat, starting at the cavity opening by the legs. You will want to loosen the skin over the breast area (from the cavity to the neck) and around the joint where the thighs meet the body. Be very careful not to puncture the skin. Do not worry about the back of the duck
Step 3Place the duck on a rack in the sink. When the water is boiling, remove from heat and begin ladling the water over the outside of the duck; you will notice the skin begin to tighten as it comes in contact with the hot water. Turn the duck over and repeat, ladling hot water until you see the skin tighten. Dry the duck well, and place it on a rack over a rimmed baking sheet.
Step 4In a small bowl, combine the salt, pepper, molasses and ground mustard to form a paste. Massage this paste over the entire outer surface of the duck, coating the skin until it looks tanned. Place the duck, uncovered, in the refrigerator and chill at least 12 hours, preferably 24.
Step 5Remove the duck from the refrigerator 1/2 hour before roasting. Heat the oven to 450 degrees, and place a rack at the lowest position of the oven to give the duck enough room to stand as it roasts.
Step 6Place a beer can chicken holder on a rimmed baking sheet or shallow roasting pan. Stand the duck on the beer can chicken holder (if the holder is too small to support the duck, first place an empty beer can in the holder), and fold the wings behind the neck. Carefully move the duck to the oven.
Step 7Roast the duck for 15 minutes to give it time to begin to color. If the duck colors too quickly at the top, tent the top of the duck loosely with foil. After 15 minutes, reduce the heat to 350 degrees and continue to roast until the duck is a rich brown color, about 1 hour. Remove from heat and set aside to rest for 10 minutes before carving.