FOOD & DRINK / On the shelf: Lemon Grass

YOU READ about it. You saw it in the supermarket. You bought it. And it stayed in your cupboard, or in a bag in your fridge. Continuing our series on items bought for a specific dish and then left on the shelf, this week, lemon grass.

Lemon grass is one of the principal spices of Thai cooking, along with chillies, ginger, coriander and kaffir lime leaves (pungent leaves usually available only from specialist shops). It is tropical grass, scented like lemon peel, though not as bitter in flavour. Some consider that is also has a slight scent of mint. When it is cooked it develops a spicy taste, akin to ginger. In Thai cooking it is used to spice soups, sauces and stocks, and to flavour most curries.

The best guide to Thai spicing is Vatch's Thai Cookbook, by Vatcharin Bhumichitr (Pavilion pounds 17.99); he is a cookery writer and restaurateur, owner of Chang Mai in Soho and the new Thai Bistro in Chiswick, west London.

Vatch says there are two ways to use lemon grass. The first is purely as flavouring, the stems cut into several pieces, pounded or crushed, then cooked in liquid or stock to release its flavour, after which you discard it.

Alternatively, and especially if the lemon grass is very fresh, strip away the tough outer leaves and discard them. Chop the tender central stem into thin rings and include in a stir-fry of vegetables, or mixed with other spicy ingredients (to smother a dish of steamed crab or fish, for example).

To preserve the fresh stems, slice and freeze them. They can be used straight from the freezer in any dish. Vatch suggests chicken breasts marinated with crushed lemon grass and chopped fresh green chillies, soy sauce, sugar and salt, steamed for 15 to 20 minutes. Or crab salad: a steamed crab, dressed with chopped lemon grass, lime juice, chilli powder, spring onions, soy sauce, Thai fish sauce - Nam pla: available from Chinese stores. Blue Dragon Chinese sauce or Amoy fish sauce can be substituted - and, if you can get them, kaffir lime leaves.

This is Vatch's recipe for the famous sweet and sour Thai soup Tom Yam Gung; in a Thai home or restaurant it would include a home-made, very hot seasoning flavoured with dried shrimps called Nam Prik Pow, but in this recipe we give chilli oil in its place.

SWEET AND SOUR SOUP

(Tom Yam Gung)

Tom yam is a basic method of making soup and you can use it with various ingredients other than prawns: mussels, scallops, crab claws, chicken pieces or thinly sliced beef.

16fl oz/500ml chicken stock

1 tablespoon chilli oil

2 kaffir lime leaves, finely chopped

2in/5cm piece of tender lemon grass, roughly chopped

3 tablespoons lemon juice

3 tablespoons fish sauce (Nam Pla)

1-2 small fresh red or green chillies, finely chopped

1/2 teaspoon sugar

8 straw mushrooms, halved (tiny button mushrooms will do)

8oz/250g small raw prawns/shrimp, peeled and de-veined

Heat the stock and chilli oil, adding the lime leaves, lemon grass, lemon juice, fish sauce, chillies and sugar. Bring to the boil and simmer for 2 minutes. Add mushrooms and prawns, stir and cook for a further 2-3 minutes or until the prawns are cooked. Turn into soup bowls and serve.