Chicken and prawn tom yum soup

Name: Chicken and prawn tom yum soup
Prep time: 30 min
Cook time: 1 h
Total time: 1 h 30 min
Cuisine: Asian, Thai
Ingredients: 1 litre/2 pints chicken stock; 300ml/11fl oz water; 6 sticks lemongrass, lightly crushed; 4 fresh coriander roots, crushed; 110g/4oz fresh galangal, peeled and sliced (available from Asian supermarkets); 8 tomatoes, cut into quarters, seeds removed; 6 lime leaves; 1-2 limes, juice only; 75ml/3fl oz tamarind water (tamarind is available from Asian supermarkets. Soak the tamarind in hot water and push the pulp through a sieve to make tamarind water.); 3 red chillies, thinly sliced; 75ml/3fl oz fish sauce (nam pla), or to taste; 75g/3oz palm sugar (available from Asian supermarkets), use brown sugar if unavailable; 12 raw tiger prawns, shelled, gutted and split in half; 2 boneless skinless chicken breasts, cut into chunks; 1 small bunch fresh coriander, leaves; 1 small bunch fresh Thai basil, leaves (available from Asian supermarkets); lime wedges