Place the duck soup set, the duck legs in a deep pot and pour in the stock. Add the soy sauce, mirin sauce, sliced ginger, garlic cloves, halved chili pepper, dried mushrooms and star anise. Cover the pot and bring to a boil. Reduce heat and simmer for 90 minutes, skimming off the foam from the surface periodically.
Take out the meat and bones to a plate, leave to cool for a few minutes and remove the meat from the bones, shredding it into pieces.
Increase heat and simmer the stock for 30 minutes until reduced by about 1/3. Add the sugar, salt and pepper. Stir and strain the stock through a fine sieve. Return to the pot and bring to a boil. Add the noodles and cook for 3 minutes.
Divide the noodles into serving bowls and top with the meat, sliced mushrooms and pour in the broth. Garnish each serving with fresh coriander, spring onion and a slice of lime and serve immediately.