For the miso sauce and marinade: Combine the mirin and sake in a pot and bring to a boil to burn off the alcohol. Add the sugar to the mixture and dissolve. Add the miso and cook until a light caramel color is achieved. Remove from the heat and cool completely. Once completely cooled, separate out the amount desired for drizzling on the burgers.
For the cod: Rinse and pat dry the cod fillets before marinating. Take the remaining amount of miso marinade and rub it over the fish. Cover and marinade in the fridge for 2 days.
For the amazu dressing: Combine the sugar, rice vinegar, salt and kombu in a pot and bring to a simmer to mix thoroughly. Remove from the heat, cover and refrigerate for 24 hours. After 24 hours, remove the kombu.
For the amazu salad: Toss together the arugula, radishes and pickled red ginger in a large bowl. Toss with the amazu dressing.
Remove the cod from the fridge and remove any excess miso marinade off the fish. Broil on medium-high heat until golden brown, 3 to 4 minutes.
For the burgers: Toast the brioche buns. Add 1 piece of broiled cod fillet and drizzle the reserved miso sauce over the fillet. Top with 1 cup of the amazu salad.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.
Recipe courtesy of Kenji Burger, Kapaa, Kauai, Hawaii