TWO DAYS PRIOR: Make the marinade. Add the mirion sweetened sake to a small saucepan over medium high heat and bring to a boil. Once it starts boiling, add the miso paste and turn the heat down to medium low. Whisk together for a bit and add the sugar. Continue to whisk it to combine it well. Once everything has dissolved, remove from heat.
Place your fish into a container that can be sealed tightly. Pat them dry. Add all of the miso sauce on top being sure that no fish is exposed. Close the container and keep in the fridge for atleast 8 hours and preferably 48 hours.
BAKE:Move your oven rack to the highest level and turn on the broiler. It should be about half a foot from the top. Using an oven proof skillet, heat up some oil over high heat. Remove your filets from the marinade. Lightly wipe off any excess marinade but don't scrape it off.
Place your fish skin side up on the skillet and cook for 3 minutes. Flip over and cook another 2 minutes.
Transfer pan to the oven and broil for 5-6 minutes. Keep a watchful eye to ensure they do not burn!!