Mahleb is made from the seeds of the wild cherry tree and used almost exclusively in sweets. Its flavor has notes of bitter almond and cherry. It is particularly popular in the Middle East and widely cultivated in Syria and Iran. In Greek cuisine it's used mainly in holiday breakfast breads and is thus considered an alternative to Chios mastic although the two spices are quite different in flavor. This spice should be used sparingly as its flavor is quite intense. Try with fresh or stewed fruit.