½ cup miso
⅓ cup mirin (Japanese sweet rice wine)
¼ cup sake (Japanese rice wine)
3 tablespoons firmly packed brown sugar
2 tablespoons soy sauce
1 ½ pounds salmon fillets
2 heads baby bok choy, halved lengthwise, or more to taste
Stir miso, mirin, sake, brown sugar, and soy sauce in a shallow dish. Add salmon fillets; turn to coat. Marinate at room temperature, 10 to 15 minutes, or in the refrigerator for up to 2 days.
Set oven rack about 6 inches from the heat source and preheat the oven's broiler.
Line a baking sheet with aluminum foil. Transfer fillets onto the baking sheet, reserving marinade.
Place bok choy in the marinade; turn to coat. Arrange bok choy next to salmon on the baking sheet, reserving marinade.
Broil in the preheated oven until salmon is lightly charred on the edges, about 4 minutes. Flip salmon and bok choy; brush with reserved marinade. Continue cooking until salmon is browned and flakes easily with a fork, about 3 minutes. Transfer salmon to serving plates. Continue cooking bok choy until it is tender-crisp, 3 to 4 minutes more.
