How to Make It
Soak the hijiki seaweed in cold water for 20 minutes. Drain and set aside.
In a medium sauté pan, heat the grapeseed oil over medium-high heat. Slit the skin on the top of the salmon to prevent the salmon from buckling. Sauté the salmon, skin side down, for 1 1/ 2-minutes. Turn and cook for 30 seconds or so. Season with salt and pepper and remove to a warm place.
In the same pan, melt 1 tablespoon of butter, add the leeks and turn the heat down to medium. Stew the leeks for 2 minutes or so until they soften. Add the Preserved Ginger and deglaze with rice vinegar. Add the mirin and Fish Stock, bring to a boil and remove from heat. Stir in the hijiki seaweed and the oysters, allowing the oysters to just warm through. Add the shiso, whisk in the remaining tablespoon of butter and season to taste with salt and pepper.
Spoon the oysters and leeks evenly into 4 warm bowls, place a piece of salmon on top and spoon in the broth.