Pour the stock into a wok and bring to the boil. Reduce the heat to medium, add the star anise, ginger and chicken and poach the chicken for 15–20 minutes, or until cooked through. Remove the chicken with a slotted spoon and cool. Leave the stock in the wok.
Bring 2litres (8cups) water to the boil in a large saucepan and cook the noodles for 3 minutes. Drain and refresh under cold water.
Cut the chicken across the breast into 5mm (¼inch) slices. Return the stock to the boil and add the asparagus, ginger, soy sauce, rice wine, sugar and ½teaspoon salt. Reduce the heat, add the noodles and simmer for 2 minutes. Add the chicken and heat through for 1 minute.
Remove the noodles from the liquid with tongs and divide among serving bowls. Divide the chicken, asparagus and spring onion among the bowls, then ladle the broth on top. Drizzle with sesame oil and serve with soy sauce.