Homemade pork and prawn dumplings

Name: Homemade pork and prawn dumplings
Prep time: 2 h
Cook time: 30 min
Total time: 2 h 30 min
Cuisine: Chinese
Ingredients: 100ml/3½fl oz freshly boiled water; 3 slices fresh root ginger; 1 tsp Sichuan peppercorns; 4 cinnamon sticks; 10 star anise; 250g/9oz dumpling flour (high-gluten wheat flour), plus extra for dusting; 2g salt; 400g/14oz pork mince (40% fat, or the highest fat content available); 1–2 tbsp lard, chilled or frozen (only if using pork mince with 10–20% fat); 200g/7oz raw prawns, heads removed, shells removed, de-veined and roughly chopped; 50g/1¾oz fresh root ginger, peeled and grated; 2 small onions, finely diced; 2 spring onions, finely diced; 1 egg, beaten; 3 tbsp sesame oil; 2 tbsp dark soy sauce; 1 tbsp light soy sauce; 1 tbsp sugar; 2 tsp salt; ½ tsp freshly ground black pepper; 1½ tbsp black vinegar (chinkiang vinegar); 1 tbsp crispy chilli oil; handful chopped fresh coriander leaves