Step 1: Prepare the marinade by bringing the sake and mirin to a boil in a small saucepan over high heat. Let it boil for 20 seconds to evaporate the alcohol.
Step 2: Turn the heat down to low and add the miso paste. Whisk until the miso has dissolved completely. Add the sugar and whisk until it is fully incorporated into the mixture for your easy miso black cod nobu.
Step 3: Remove from heat and let the marinade cool completely to room temperature. This is crucial to prevent partially cooking the fish during the marinating process.
Step 4: Pat the black cod fillets completely dry with paper towels. Place them in a non-reactive container and pour the cooled marinade over them, ensuring every side is coated.
Step 5: Cover and refrigerate the easy miso black cod nobu for 2 to 3 days. Flip the fillets once or twice during this time to ensure even absorption.
Step 6: When ready to cook, preheat your broiler to high. Lightly wipe off excess marinade from the fillets using your fingers.
Step 7: Place the fish on a foil-lined baking sheet or in a cast iron pan. Broil 6 inches from the heat source for 10-12 minutes, or until the surface is caramelized and charred and the fish flakes easily.