Preheat your oven to 325F.

Score the thick fat on all sides of the duck in a diamond pattern, being careful not to slice through the meat.

Place the duck on a roasting rack, and place the rack in am aluminum-foil-lined roasting pan, or other baking dish with at least 2 inch high sides. (You don't want the duck sitting in its rendered fat. A roasting rack will get it off of the bottom of the pan, allowing the fat to collect below.)

Roast the duck for 3 hours. Every hour, re-slash the fat and flip the duck over. (You can drain any fat from your roasting pan at each hour, or just wait to collect it all at the end.)

The duck is cooked when the juices run clear and the leg bone moves easily in the socket.