The flavor of fresh Kaffir lime leaf is so particular and so citrusy and floral, there’s really no substitute—though you can attempt a mix of ordinary lime zest and lemongrass. Thankfully, the leaves are available, if not from your local Asian grocery, online (try kaffirlimeleaves.com), or if you become a real diehard, from the live tree you keep in a pot in a sunny window.

David TanisNYtimes Blog Writer