Take 700 g slab skinless pork belly and pierce both sides with a fork.
Dry the pork belly with a paper towel and roll. Start with the thinnest side and roll it up, secure with string or meat netting. (See video for how to tie with string.)
Place the pork into a deep pot, fill with cold water until the pork is just about submerged. (It's okay if the highest part is slightly poking out the top.)
Turn the heat on a medium-high setting and bring the water to a boil. If any scum floats on the top, scoop it out.
Once it's boiling, lower the heat to a simmer and add 50 g Japanese leek (naganegi), 100 g onion, 50 g ginger root, 3 cloves garlic and 1 tsp rice vinegar.
Once the time has passed, remove the drop lid, carefully flip the pork over onto the other side and place the drop lid back. Simmer for another hour.
After the time is up, turn off the heat, remove the pork from the broth and place it in a large ziplock bag.
Part 2
Scoop 250 ml pork stock leftover from the pot and pour it into a saucepan.
Add 50 ml sake, 1 tbsp mirin, 150 ml Japanese soy sauce (koikuchi shoyu) and 30 g sugar to the pan and boil for 1 minute.
Turn off the heat and leave it to cool slightly. Once cooled, pour it into the ziplock bag with the pork. Seal the bag and marinate in the fridge for at least 12 hours (preferably overnight).
Part 3
Heat a frying pan on a medium-high heat. Once it's hot, add the pork belly to the pan and lightly char the outside. Keep turning the pork to make sure all the edges are evenly charred.
Transfer the pork to a plate and pour 100ml of the leftover chashu marinade into the pan.
Allow the sauce to thicken slightly and place the pork back in.
Keep turning the pork to coat the surface with the glaze. Once fully covered, remove it from the pan and allow it to rest for 5-10 minutes.
Remove the rope or net and then cut the chashu into slices.
Remove the ginger, spring onion and garlic at the end of the simmering time and store leftover pork stock in the fridge for up to 1 week or 1 month in the freezer. You can use it for soups and broths.
You can soak boiled and peeled eggs in the ziplock bag with the leftover broth to make ramen eggs. Scoop out the pork fat before adding the eggs.
The chashu pork can be kept in the fridge for 3 days or 1 month in the freezer. I recommend slicing it first for convenience.
Rolling the pork belly is for decoration and is optional. You can still make delicious chashu without rolling it. If you don't roll it, reduce the cooking time to 45 minutes on each side. (1 hour 30 minutes total)