Sumiso

1/4 cup shiromiso
2 tablespoons sugar
2 tablespoons sake
2 tablespoons water
1 1/2 tablespoons rice vinegar
2 teaspoons hot english mustard

sliced scallions for garnishing

Combine all ingredients in a saucepan and bring to a boil, stirring. Remove from heat and let cool. (This mixture keeps for 2 months in the refrigerator.)

Preheat broiler or grill.

Place mussels on broiler pan — crumpled foil or a bed of coarse salt will keep them steady. Broil until slightly brown and surface is drying out, about 5 minutes. Spoon sumiso sauce on mussels and broil for 1 minute. Transfer to plates and garnish with sliced scallions (which I didn’t use here because my kids didn’t want it).

from Japanese Home Cooking
By Shunsuke Fukushima