Thinly slice 25g of ginger.

Cut leek in 2” sections.

Combine 2 cups of water, ½ cup of soy sauce, ¼ cup of sake, ¼ cup mirin, and 4 tablespoon sugar in pot.

Add ginger and leek into pot.

Bring to a boil.

Tightly roll 1 ½ lbs of pork belly and tie with cooking twine.

In a pan and 1 tablespoon of oil and cook pork belly on medium high heat.

Turn as color changes.

Remove from heat when all sides are colored.

Place pork into sauce.

Bring to boil on medium heat and cover with otoshi buta.

Cover with lid and cook for 15 minutes.

Rotate pork.

Reduce heat to low.

Cover and cook for 2 hours, turning pork every 10-15 minutes.

Set aside to cool.

Remove pork and scoop out fat from sauce.

Strain sauce.

Remove cooking twine and cut into thin slices.

Plate and pour sauce over chashu.