Peel and chop the potatoes into bite-sized pieces. Soak in water for 5 minutes, then drain. Slice the leek into 4cm pieces, separating the green and white parts.

Pat the salmon fillets dry with a paper towel and cut them into thirds.

Heat salad oil in a frying pan over medium heat. Place the salmon skin-side down and add the white parts of the leek. Cook until both sides are browned.

Add the potatoes and broth ingredients (water, sake, mirin, ginger). Bring to a boil, cover, and simmer on low heat for 7–8 minutes.

Add soy sauce and miso, stirring until the miso dissolves. Cover and simmer for another 5 minutes. Remove the lid and cook on medium heat for 2–3 minutes to thicken the sauce.