The cornelian cherry is the tart red fruit of Cornus mas, a dogwood — not a true cherry at all, but an olive-shaped, jewel-red drupe about the size of a small acorn, with a single hard stone and a sharp, mouth-puckering acidity that softens as it ripens. It is a cornerstone of the Caucasus, Iran, Turkey and the Balkans, where it is turned into sharbat, jams, sauces, a sour seasoning and the fruit leather sold across the region.