To prepare Sichuan pepper and salt mixture, place peppercorns and salt in a small frying pan and dry fry until mixture becomes fragrant and peppercorns being to ‘pop’. Allow to cool, then use a mortar and pestle to grind, set aside.
To prepare the duck, rinse under cold water. Trim away excess fat from inside and outside of cavity. Remove neck, parson’s nose and winglets and discard. Pat duck dry and rub with Sichuan pepper and salt mixture. Place duck in a large lined steamer basket and tightly cover. Steam over a large saucepan of boiling water for about 1 hour 15 minutes or until duck is cooked through (to test if cooked through, insert a knife between leg and breast – the juices will run clear). Transfer duck to a large tray and cool slightly. Place in the freezer until cold. Place duck, breast side up onto a chopping board. Using a large knife or cleaver, cut duck in half lengthways, through the breast bone and back bone. Ease meat away from carcass, leaving thighs, legs and wings intact; discard carcass. Lightly dust the duck halves in flour to coat, shaking off any excess. Pour oil into a hot wok until heat until hot. Deep-fry duck halves, one at a time, for about 3 minutes each side or until brown and crisp. Remove duck from wok and drain on absorbent paper towel. Rest for 5 minutes and cut duck into pieces
To prepare the citrus sauce, combine the water and sugar in a small saucepan and bring to boil. Reduce heat and allow to simmer, stirring occasionally for about 7 minutes to reduce slightly. Add fish sauce and spices and simmer for a further minute. Stir through lime juice and orange and remove from heat.
To prepare sung choi bao, refresh lettuce leaves in iced water, drain and refrigerate until required. Using a vegetable peeler, thinly slice carrot lengthways into ribbons. Cut carrot into a fine julienne and set aside. Heat oil in a hot wok and swirl to coat. Add ginger, garlic and onion and stir-fry for 1 minute until fragrant. Add mushrooms and stir-fry for 1 minute until soft. Add wine, tamari, sugar and sesame oil and stir-fry until heated through. Add reserved carrot, celery, bean sprouts and spring onions and toss to combine.
To serve, reheat duck sauce. For sung choi bao, spoon vegetable stir-fry into lettuce cups and garnish with coriander. Pour hot citrus sauce over duck pieces and serve with sung choi bao.