Miso Glazed Chilean Sea Bass

0 Make the Marinade: Boil the mirin and sake for 3 minutes. Add the sugar and miso and cook a couple of minutes over medium-low, without letting it boil. Let it cool completely.
1 Marinate: Pour the cooled marinade over the sea bass, cover it very tightly, and refrigerate for 24 to 48 hours.
2 Broil: Position an oven rack about 6 inches from the broiler and preheat the broiler to high. Line a baking sheet with foil. Broil for about 7 minutes, until the top caramelizes and the fish is opaque and flakes easily, about 135°F (57°C). Watch closely because the miso and sugar darken quickly.
3 Finish: Add the leftover marinade to a saucepan and boil for at least 5 minutes, stirring frequently. Brush over the cooked fish before serving.