Add the saikyo miso, sake, and mirin into a small glass pan.
Mix the ingredients together with a spoon until smooth.
Set the marinade aside.
Rinse the fish fillets with cold water.
Pat fillets dry with paper towel.
Lightly cover both sides of fillets with salt.
Add both fillets to the glass pan. Use a spoon or gently turn over the fish to cover both sides of fillets with the marinade.
Cover the pan with a lid and keep in the refrigerator overnight.
Grilling fish
Preheat fish grill at medium heat or oven (varies by cooking method).*
Lightly wipe off most of the miso marinade.
After your grill heats up for a few minutes, add fish to the center of the grill.
Once the top of the fish fillets begin to brown (3 - 4 min), turn over fillets using a wooden chopsticks or spatula.
Cook until the other side begins to brown (2 - 3 min).
With chopstick or fork, check to see that the inside of the fillets are fully cooked (white in color and not translucent).
Remove from stove and serve hot.
Asparagus with Moromi Miso
Trim off the ends of the asparagus.
Bring one inch of salted water to a boil in a large skillet.
Cook asparagus for 3-5 minutes, just until tender. It depends on the thickness of the spears. Test tenderness by poking with a fork.
Drain water.
With a spoon, spread the moromi miso into the middle of your plate.
Place asparagus spears on top of the miso with the tips all pointing one direction.
Season with sea salt.
Then, place your hot fillet of fish on the front portion of the moromi miso with one end overlapping the the asparagus.
Notes
*If you don't own a fish grill, follow these directions:1) Preheat oven to 400°F.2) Heat a cast iron or other oven-proof skillet over high heat on the stovetop.3) Film the pan with a thin layer of oil.4) Place the fillets skin-side-up on the pan and cook until the bottom begins to brown, about 2-3 minutes depending on the size of fillet.4) Gently flip fillets with a spatula. Cook the other side until browned, 2 to 3 minutes. Transfer to the oven and bake for 4 to 10 minutes, until fish is opaque and flakes easily.