1/2 cup loosely packed bonito flakes (katsuobushi)*
1 large leek, white and pale green parts only, sliced and rinsed well
2 medium carrots, peeled and cut into 2-in. matchsticks
1 1/2 pounds black cod or Pacific halibut, cut into 1 1/2-in. pieces
3/4 pound medium sea scallops (15 to 16 per lb.)
3/4 pound medium shrimp (26 to 30 per lb.), peeled, tails left on if you like
1/2 cup shiro (sweet white) miso
1/2 cup lager (preferably Longboard)
Lemon zest (optional)
Thinly sliced shiso leaf* (optional)
How to Make It
Bring 4 cups water, the ginger, and kombu to a boil in a large, wide pot. Reduce heat and simmer, covered, 4 minutes. Turn off heat, sprinkle in bonito flakes, and let sit 3 minutes (flakes will sink). Strain broth through a cheesecloth-lined fine-mesh strainer into a bowl.
Rinse pot, then pour in broth. Add leek and carrots. Bring to a simmer and cook 2 minutes. Add black cod and scallops; simmer 1 minute. Add shrimp and cook 2 minutes more.
Whisk miso with lager in a small bowl. Remove stew from heat and carefully stir in miso mixture. Serve with lemon zest and shiso for topping if you like.
*Find kombu, a large seaweed sold dried, and bonito flakes with the Asian ingredients at well-stocked supermarkets and at natural-foods or Japanese markets. Find shiso, an aromatic herb, at Japanese markets and some farmers' markets.