First make the Japanese soup stock, or dashi: In a 4-quart saucepan, combine 3 quarts of water, the kelp, and bonito flakes and place over medium-low heat.

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First, the primary dashi, which functions as this soup's broth, comes together when a pot of water with kombu is boiled and bonito flakes are tossed in.

WSJ: Amaryll Schwertner's Poached Halibut in Dashi With Leeks, Sweet Potatoes and Sesame Seeds | Slow Food Fast

Now for what Ms. Schwertner calls the secondary dashi, which serves as the poaching liquid for the halibut: Add the reserved bonito flakes and kombu to a pot with water and Meyer lemon slices.

WSJ: Amaryll Schwertner's Poached Halibut in Dashi With Leeks, Sweet Potatoes and Sesame Seeds | Slow Food Fast

It is traditionally made with water, kombu, a dried seaweed, and dried, smoked bonito fish flakes.

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Choose your own ingredients from tender squid, plump prawns or juicy pork, topped off with bonito (fish) flakes, a thick brown okonomiyaki sauce and mayonnaise.

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To make this dashi, simmer kombu (a dried seaweed) and bonito (dried tuna belly flakes). (Both ingredients are available at most Japanese markets and some specialty stores.) If you can't find kombu, Ms. Schwertner suggests using dried shiitake mushrooms, which impart a similar umami flavor.

WSJ: Amaryll Schwertner's Poached Halibut in Dashi With Leeks, Sweet Potatoes and Sesame Seeds | Slow Food Fast