Step 1

Boil sake and mirin over high heat and reduce by 1⁄3.

Step 2

Turn heat down, add miso and sugar, and cook for 2 to 3 minutes, stirring constantly to prevent burning.

Step 3

Cool to room temperature.

Step 4

Marinate cod fillets in the miso mixture for 4 days.

Step 5

Gently wipe off excess marinade from the fillets and grill or broil until well browned.