Pistachio

The pistachio is the edible seed of Pistacia vera, a small desert tree of the cashew family whose ripe fruit splits its shell open along a natural seam — the "smile" that lets you thumb it apart. Inside sits an oblong kernel coloured a vivid chlorophyll green and wrapped in a thin, papery skin that shades from mauve to deep purple. Raw, it is faintly resinous and sweet; roasted, it turns deeply nutty, buttery and toasty. It is the only nut prized as much for its colour as its flavour, and the only one sold still smiling in its shell.