Teriyaki Salmon

For the teriyaki sauce: Combine the soy sauce, mirin, sake and sugar in a bowl. Add the mixture to a large nonstick skillet and bring to a light simmer over medium heat, stirring gently, until the sugar is dissolved. Remove from the heat. Transfer to a bowl and set aside to let cool. Wipe out the skillet with a paper towel.

For the salmon: Sprinkle each salmon fillet with salt and pepper. Put the potato starch in a bowl and season with salt and pepper. Lightly dust each fillet with potato flour all over.

Set a skillet over high heat until hot, then add the oil. Add the salmon and fry each side until golden brown all over, 3 to 4 minutes total. Remove the salmon to a plate.

Add 1/2 cup of the teriyaki sauce to the skillet. Transfer the remaining sauce to an airtight container and reserve for another use; the sauce will keep up to 3 weeks in the refrigerator. Bring the sauce in the skillet to a boil over medium heat, then immediately reduce the heat and bring to a simmer. Cook until the sauce is reduced by half then return the salmon to the skillet and warm through. Turn off the heat and spoon the sauce over the salmon.

Sprinkle the salmon with spring onions and serve.