Clean the fish with a paper towel soaked with 2 Tbsp sake.
In an air tight container that would fit the fish, combine all the Seasonings.
Mix well and make sure miso is all dissolved.
Marinade the meat for overnight.
With your fingers, remove the marinade off the fish completely. Do not leave excess miso on the fish; otherwise, the fish will burn easily. Place the fish skin side up on a baking sheet lined with parchment paper/silicone mat (for baking) or foil (for broiling).
To Broil (Recommended)
Preheat the broiler* with a rack placed about 6" (15 cm) away from the top heating element (in the middle) for 3 minutes. Broil medium/high for 8-10 minutes, depending on the thickness of the fish, until the surface is blistered and brown a bit. You do not need to flip it. *Typical broiler setting: Low/450ºF/232ºC, Medium/500ºF/260ºC, and High/550ºF/288ºC. I use medium (6" or 15 cm away) or high (8" or 20 cm away).
To Bake (Optional)
Preheat the oven to 425°F (218ºC) with a rack placed in the middle. For a convection oven, reduce cooking temperature by 25ºF (15ºC). Bake the fish on parchment paper until the surface is blistered and brown a bit, about 15-20 minutes. You do not need to flip.
You can keep the leftovers in an airtight container and store in the refrigerator for up to 2 days or in the freezer for 2 weeks.