Mix the chicken with the soy sauce, rice wine, ginger, garlic and a pinch of salt in a large bowl. Put in the fridge and leave to marinate for at least 1 hr or ideally overnight. Meanwhile, make the sauce. Tip the rice wine, vinegar and sugar into a saucepan with a pinch of salt and bring to the boil. Stir until the sugar has dissolved, then add the garlic and ketchup. Continue to cook for 10 mins until syrupy, then remove from the heat and set aside. To prepare the toppings, put the coriander and spring onion in a bowl of iced water to perk them up. Toast the peppercorns in a dry frying pan, if using, then crush using a pestle and mortar. Mix with 1 tbsp sea salt and set aside.