Use a very large saucepan and bring the water to a boil.
Add the bones, ginger, carrot and leek then turn heat to medium low and boil for at least 2 hours. Boiling for longer is better but the longer you boil the more water you’ll need to add to maintain the volume as the soup evaporates. The water should only reduce by about 40% before you strain and serve as ramen soup.
During boiling be sure to remove scum from top; about every 20 minutes.
After approximately 1 hour of boiling add soy sauce, oyster sauce and sake.
Once boiling is completed strain soup through cloth towel and this should remove all the scum from the soup.
Pour strained stock into fresh saucepan and bring to boil adding salt, pepper and sugar for taste. If needed also add extra sake and/or soy.
Serve the soup hot with noodles and garnish with freshly diced spring onions or leeks, nori (seaweed), bean sprouts, boiled egg and some char siew pork.