Water chestnuts aren't the easiest vegetable to deal with: they're often covered in mud (as they're grown in shallow ponds), their tough, firm skin needs to be trimmed off and, occasionally, they are mouldy inside. However, there's no substitute for water chestnuts, because they have a unique, sweet taste and a firm, crunchy texture that's an essential ingredient in many Asian dishes. When buying them, press on all sides to make sure they're firm. If they're soft, they might be mouldy. Cut off the top and bottom of the chestnut with a sharp paring knife, then remove the rest of the skin. Some wet-market vendors sell them pre-peeled and sitting in a bowl of water, which makes them more convenient to use, although be sure to rinse them thoroughly. Don't buy canned water chestnuts - they have no flavour and only the faintest crunch. One of my favourite ways to eat water chestnuts is in a Thai dish where they're cooked with fresh shrimp in a sweet, mildly spicy sauce. Make a paste by pounding small spicy red chillies (seeds removed) and larger, mild chillies in a mortar with garlic, fresh coriander roots and chopped lemongrass. Mix the paste with fish sauce, sugar, a little white pepper and some tamarind paste. Heat oil in a wok and fry the paste until fragrant. Add the shrimp (head and shells removed) and peeled and sliced water chestnuts. Stir-fry constantly until the shrimp are pink and curling, and the sauce lightly coats all the ingredients.