Don't cut off any of the fat or skin before cooking.
Fill a very large pot with cold water and place the leg into it. Bring it slowly up to a simmer and try and remove any coagulated fats and blood that will rise to the surface. This is the only real work there is in this recipe and you don't have to be fanatical about it.
Once the meat has come to the boil, turn it down and simmer covered very gently for 2½ hours.
While the meat is cooking make the sauce by simply putting all the ingredients into a small bowl and mixing them together well to dissolve the sugar.
When done, pour off the water and move the leg to a cutting board or a large dish. Let cool a little so you can handle it. Using a knife but your fingers will be better pull off the skin and any extra fat that is under it. Then pull off the meat from the bone, pulling away any bits of fat that will be in between the meat. Break it up as you go. I do this using my fingers and a fork.
While the meat is still warm place on a serving plate. Take some of the sauce and pour it over the meat and mix it together and its done.