How to Make It
Pat the fish dry with paper towels, then rub all over with shio koji. Cover and refrigerate for 2 hours.
Warm 1 tablespoon of the butter in a skillet over medium heat. Add the chopped kale and toss briefly, then add the vinegar. Toss until the kale is softened and bright green, then toss in the togarashi and a dash of salt. Set aside.
Warm the remaining 4 tablespoons butter in a skillet over medium heat. Remove the fish and wipe away the excess shio koji. Combine the potato starch and white pepper, then dredge the fish in the starch. Pan-fry the fish, in batches if needed, about 3 minutes per side. The fish is done when it is just starting to flake. Serve the fish over a bed of the sautéed kale.