Preheat the oven to 200°C.
Mix marinade ingredients in a bowl and coat the duck for at least 20 minutes.
Sear duck skin-side down in a warm frying pan for 10 minutes until golden.
Flip duck over and cook for one minute on high heat until crisp.
Roast duck in the oven for 15 minutes.
Rest duck for five minutes before slicing.
Simmer chicken stock with mushrooms, soaking liquid, and Chinese leaf.
Add soy sauce, rice wine, vinegar, and udon noodles to the pot and boil.
Stir in spring onions, bean sprouts, and coriander, then season.
Ladle soup into bowls and top with sliced duck to serve.