Sichuan pepper is not actually pepper, but the dried red-brown berries of a type of ash tree that have a lemony, peppery aroma. Sichuan pepper has the characteristic ‘mouth-numbing’ quality typical of many dishes from the Sichuan province of China. It is also one of the spices used in Chinese five-spice powder.
Sichuan pepper is sold as whole berries or a ground powder. Try to buy the freshest berries you can, as they quickly lose their pungency.