Pound the unpeeled ginger in a mortar and pestle and add to a very large pot containing about 1 gallon of water, along with the tops of the spring onions used for the ginger and spring onion oil.
Add the salt and MSG or chicken stock powder (if using) and bring to the boil over high heat.
Taste the water and adjust the amount of salt so that it tastes savory and a little salty.
Reduce the heat to very low and add the chicken to the pot.
There should be enough water in the pot so that the chicken doesn’t touch the bottom of the pot, as that will cause the skin to tear.
Using Poultry hooks, lift the chicken in and out of the water a couple of times to get the liquid in the chicken’s cavity.
If you have poultry hooks, use them to hang the chicken in the pot.
The water should now be steaming but not bubbling. Keep the heat low at this level and cook the chicken for 45 minutes.
Using the poultry hook (or slotted ladle), carefully lift the chicken out of the pan, ensuring you don’t break the skin, and plunge into a large bowl or sink of salted iced water.
Reserve the stock and stand the chicken in the iced water for at least 10 minutes, turning once. This will stop the cooking and give the skin its delicious gelatinous texture.
Remove from the iced water and hang over a bowl or the sink to drain well.
Rub the skin all over with the sesame oil.
The chicken should be cooked very lightly, pink inside the bones and with a gelatinous skin.