Time until ready: ~6 months
375g sea salt plus 1 tbsp for sprinkling
Rinse beans. Soak overnight in 3x the amount of water. Cook on medium heat until soft. Strain, reserving 1 cup of bean cooking liquid. Allow the beans to drain in a colander until warm and not too hot to handle.
Meanwhile, in a large bowl, combine the koji and sea salt with your hands.
In another large bowl mash the warm beans by hand or process in a food processor for desired texture. If necessary, add a little of reserved bean cooking liquid to the beans if they are overly dry.
Now combine the warm (but not too hot) mashed soybeans into the bowl with the koji and salt mixture. Take your time incorporating all ingredients.
Form tennis-sized balls of miso, squeezing out the air, and pack tightly into a one gallon vessel. Form one layer at a time so there are no air pockets.
Clean the sides of the container when finished.
Sprinkle 1 tbsp of sea salt on top of the surface of your miso.
Place plastic wrap on the surface to protect from air. Place a heavy weight (~2 lbs) on top of the plastic wrap. Cover with loose lid and ferment in a dark, cool, dry location for at least 6 months (or longer).