Mix the miso, sake, mirin, soy and sugar in a bowl.
Place the salmon, and miso sauce in a ziplock bag and marinate in the fridge for a couple of hours or overnight.
Bake the salmon in a preheated 450F/230C oven for a few minutes (the exact time will depend on how thick the salmon is).
Broil the salmon until golden brown on top, about 1-3 minutes.
