Step 1Pat the roast dry with a paper towel and carefully score the skin into diamond shapes. This is most easily done with a small sharp knife.
Step 2Sprinkle the roast liberally with salt, about 2 1/2 tablespoons. Place the roast upright on a plate, with the shank pointing straight up. Refrigerate, uncovered, for at least 2 hours to overnight.
Step 3Heat the oven to 325 degrees. Remove the roast from the refrigerator; pat dry. Arrange on a rack in a roasting pan, skin-side up and place in the oven. Roast to an internal temperature of 150 degrees, about 2 3/4 to 3 hours.
Step 4When the meat is done, raise the oven temperature to 450 degrees for 15 minutes to crisp the skin. Remove the roast from the oven and let stand at least 20 minutes to 1 hour.
Step 5To serve, use a carving knife to slice away the cracklings, keeping them in a single sheet as much as possible. Place on a separate plate. Slice away any thick pieces of fat that may remain. Slice the meat from the bone in 1/4- to 1/2-inch pieces. This is most easily done by slicing parallel to the main leg bone, working your way around the leg. Arrange the sliced meat on a platter and place the cracklings on top.