Combine butter and miso paste together until they are completely blended. Set aside.
Pat the fish dry with paper towels. Sprinkle the fish with salt.
Heat 1 tablespoon of miso butter on a medium-hot pan. Add the fish, skin side up. Loosely cover the pan with foil ad cook for 3-5 minutes, or until lightly browned. Flip the fish and cook until cooked through. Add more butter if the pan is too dry.