Gotu kola (Asiatic pennywort) grows wild along the paddy edges in the south and centre of Sri Lanka, and a raw sambol of its leaves is the green, slightly bitter bite that balances a rice-and-curry lunch. Families in Galle and Matara will tell you it is good for the memory, and it is often served at the start of a meal or with kola kenda, the herbal porridge. The leaves are shredded as finely as possible, then tossed with shallot, tomato, green chilli, a little fresh coconut and plenty of lime, so it's crunchy, peppery and bright. Look for pennywort bunches in Sri Lankan, Thai and Vietnamese shops. The mistake to avoid is dressing it too early: the salt and lime wilt the leaves within half an hour. Chef's tip: roll a stack of leaves into a tight cigar and slice it hair-thin with a sharp knife; the finer the shreds, the better it tastes.