Curry leaf is not, unfortunately, the bouillon cube of the plant world โ it does not magically turn an ordinary sauce into a curry-flavoured hit.
The thin, delicate leaves do, however, smell like Indian curries and, when used in a complex spice mixture, add a strong fragrance and a distinct, slightly bitter flavour.
You can buy inexpensive bags of fresh curry leaves in specialist Indian produce shops, while pricier jars of dried specimens can be found in upscale supermarkets.
Do not bother with the dried ones โ usually they have lost much of their aroma and flavour. And the fresh leaves freeze well.
In addition to being used in Indian kitchens โ primarily in the south of the country โ the leaves of the Murraya koenigii plant are used extensively in Sri Lanka and more sparingly in some Southeast Asian countries, including Vietnam, Cambodia and Malaysia. They are usually fried in oil to deepen the colour and flavour.