Cook soybeans until very soft
Drain and cool the soybeans
Mash the soybeans into a paste
Mix in koji
Add salt
Add a little reserved cooking liquid if needed
Pack the mixture tightly into a clean container
Press out air pockets
Cover the surface with plastic wrap or a clean weight
Seal the container
Ferment in a cool, dark place for several months to years
Check periodically for mold or excess liquid
Stir or re-pack if needed
Taste when the flavor reaches the desired depth
Store the finished miso in the refrigerator