Tahini is a sesame paste, most often used in Middle Eastern recipes. Texturally, it is most comparable to smooth peanut butter, with the same mouth-coating property.
In the UK tahini is most commonly found along with chickpeas in hummus. In The Middle East, sesame is often associated with sweetness, as tahini makes the base of the popular confectionery, halva.
The most common type of tahini is a 'light roast', made from hulled white sesame seeds, which have been roasted and then milled. Unhulled seeds make a stronger and darker tahini, and black sesame seeds can even be used to make a dramatically-coloured paste.
Tahini's high calcium and protein levels make it a popular ingredient amongst vegan chefs, and raw tahini can be purchased at specialist or health food shops to cater for specific diets. Regular tahini is now available in most big supermarkets, and many now have own-brand versions.