Remove the remaining meat from the chicken carcass and place it in the fridge.
Heat 2 litres/3½ pints of water up to a simmer in a large, deep saucepan.
Place the roasted chicken carcass, along with any remaining cooking juices, into the hot water and add the carrots, whole leeks, onion, bay leaf, peppercorns and stock cube.
Bring the stock up to the boil, reduce to a simmer and cook for an hour. Skim the stock from time to time to remove any scum that forms on the top.
After cooking the stock for an hour, place a colander over a large pan. Pick out the chicken carcass from the stock and place it into the colander. Carefully pour the rest of the stock through the colander into the pan.
Return the strained stock to the heat, and bring back up to a simmer.
Meanwhile, tear the reserved roast chicken into small pieces.
Add the noodles to the chicken stock and cook for a minute before adding the chicken, bok choi, spring onion, sweetcorn and soy sauce to the pan. Cook for 2-3 minutes, then stir through the chopped coriander.