If necessary, roll the block of Pork and secure with kitchen string, tying at 2-3cm intervals. Do not use nylon or plastic string.
Place the Pork in a pot or a large saucepan, add just enough water to cover the Pork. Add Salt, Sake, Ginger, Garlic and Spring Onion. Bring it to the boil over high heat, then reduce the heat to low and simmer for 1.5 to 2 hours depending on the size of the Pork. Let it cool in the liquid.
While the Pork is cooking, make the marinade. Place Mirin in a small saucepan and bring to the boil, then add Soy Sauce and cook for 1 minute. Let it cool. *Note: If you don’t mind the alcohol that Mirin contains, you can just mix Mirin and Soy Sauce.
Place cooled Pork (still warm is fine) and the marinade in a suitable size ziplock bag. Remove the air in the bag as much as you can. When the pork is cool enough, place it in the fridge and rest overnight.
