1.Make primary dashi. Combine dashi granules, water, cooking sake, mirin and soy sauce in large saucepan and bring to the boil. Simmer stock, uncovered, 10 minutes.
2.Cook noodles in large saucepan of boiling water until tender; drain. Cover to keep warm.
3.Bring dashi, 2 tablespoons of the sauce, half the mirin and half the sugar to the boil in medium saucepan. Remove from heat; cover to keep warm.
4.Heat oil in medium frying pan; cook chicken and leek, stirring, until chicken is cooked through. Stir in remaining sauce, mirin and sugar; bring to the boil.
5.Divide noodles among serving bowls; top with chicken mixture, ladle over broth. Sprinkle with seven-spice mix.
You could add 1 tablespoon grated fresh ginger to the broth for extra flavour, if you like.Note