Preparation

• Combine the mirin and sake in a small saucepan and bring to a boil. Whisk in the miso until smooth, then add the sugar and cook over medium heat, stirring constantly, until the sugar has dissolved. Transfer the marinade to a bowl and cool.
• Pat the cod fillets thoroughly with paper towels and generously coat with marinade on both sides. Place in a nonreactive bowl or dish with any remaining marinade, cover tightly with plastic wrap, and refrigerate for at least 8 hours or overnight.
• Heat the oven to 400°F. Warm the oil over medium-high heat in an ovenproof sauté pan large enough to hold the fish in one layer. When the oil is hot, scrape the excess marinade off the fish and cook the fish until lightly browned on one side, about 2 minutes. Turn the fish and place the pan in the oven until the fish is cooked through and flaky, about 8 minutes. Serve on warm plates topped with the garnishes.