In a small saucepan, boil mirin and sake. Whisk in the miso until dissolved. Add the sugar and cook over medium heat, whisking until dissolved. Remove marinade from heat and place into a large baking dish and cool. Add the fish and turn to coat. Cover and refrigerate overnight.
Preheat the oven to 400°. Heat a grill pan and oil it. Scrape the marinade off the fish. (DO NOT RINSE) Add the fish to the hot pan and cook over high heat until browned, about 2 minutes. Flip the fish onto a heavy rimmed baking sheet and roast for 8-10 minutes, until flaky.
Garnish with pickled ginger.
The marinade can be made and refrigerated up to 1 week before using.
Make sure you use white miso paste. Anything thing else will be too strong. We recommend the brand Hikari Miso.
Side suggestions: Sesame sugar snap peas or baby bok choy and steamed rice.
Suggested Pairing: Spicy, full-bodied Gewürztraminer or sake.