Step 1

Add sake to a medium saucepan over medium to medium high heat. Bring to a boil for a few seconds to help evaporate some of the alcohol. (Not necessary if using cooking sake)

Step 2

Add the mirin and soy sauce and let come to a simmer.

Step 3

Add kombu and bonito flakes. Let the mentsuyu come to a boil, then reduce heat to low and simmer for about 5 minutes. Remove from heat and allow to cool.

Step 4

Strain through a fine sieve and store in an airtight container in the refrigerator for up to one month.