Mix all the ingredients for the spice rub together in a mixing bowl. Rub this mixture all over the duck legs and set on a resting rack over a sheet pan in the fridge. Cure for 24 hours.
When the cure is completed, brush off all visible spice and pat the legs dry with several paper towels. Place the legs in a casserole dish that just holds the legs with little extra space. Melt the duck fat in a sauce pan and pour over legs. It is important that the legs be completely covered in fat before cooking. Cook uncovered for 1 1/2 to 2 hours in a 280 F oven until fork tender. The legs can be kept refrigerated in the same fat it was cooked in for several weeks.
To serve the legs, remove from the fat and rub off the excess fat with your fingers. Using a cast iron skillet or non-stick frying pan, set the legs SKIN SIDE DOWN over medium/ low heat.
The fat will slowly render out. When most of the fat is rendered, pour off the excess and increase the heat. This will crisp the skin of the duck. Serve hot with a salad of mixed greens and some crusty French bread.