Asian chicken and prawn broth

Name: Asian chicken and prawn broth
Cuisine: Asian
Ingredients: 1.2 litres (2 pints) hot chicken stock, for both methods; salt and freshly ground black pepper; 1 tbsp dark soy sauce; 3 tbsp fish sauce (nam pla); 3 tbsp mirin; 1 tsp tahini; 2 garlic cloves, finely chopped; 5cm (2in) piece of fresh root ginger, peeled and sliced into fine strips; 2 tsp dried chilli flakes; 225g can bamboo shoots, drained and rinsed; 225g can water chestnuts, drained and rinsed; 125g (4oz) button mushrooms, whole or larger ones halved; 2 skinless chicken breasts, finely sliced; bunch of spring onions, finely chopped; bunch of coriander leaves; 250g pack of ready-cooked small prawns or shrimps