Cut the white stalk of the leek into 4 to 5 cm bite-sized pieces.
Combine the ingredients.
Heat oil in pan and saute the leeks.
Turn them over while lightly browning, add sake, reduce to low heat, then cover with a lid.
Once they are cooked through to the desired tenderness, add the combined ingredients, briskly coat the leeks in the sauce, then immediately remove from the heat.
Transfer to a dish, sprinkle with bonito flakes, then serve.