This is a nice light alternative to making a bisque. The Asian spices give it a lovely fresh flavour with an underlying kick of ginger. You will probably end up with more than enough broth, so I would suggest freezing any surplus.
For the broth
The shells from 1 crab, broken into smallish pieces
1 medium onion, peeled and roughly chopped
A couple of sticks of celery, roughly chopped
6 cloves of garlic, peeled and chopped
30g root ginger, roughly chopped
10 Sichuan peppercorns
Stalks from the coriander (see below)
2tsp tomato purée
2ltrs fish stock
Salt and freshly ground black pepper
2 spring onions, trimmed and finely shredded on the slant
20g very fresh root ginger, scraped and very finely shredded
A few sprigs of coriander
1tbsp chopped Chinese or normal chives
1tbsp white crab meat
Put all of the ingredients for the stock into a saucepan, bring to the boil, skim and then simmer very gently for an hour, skimming regularly. Strain the stock through a fine-meshed sieve, try it, and if it's not strong enough, just return it to a pan and simmer and reduce it until the taste improves; season to taste.
To serve, just put the garnish in warmed soup bowls and pour over the hot broth.