The sunchoke — also called the Jerusalem artichoke or sunroot — is the knobbly, edible underground tuber of Helianthus tuberosus, a tall perennial sunflower native to North America. Despite its names it has nothing to do with Jerusalem and is not an artichoke; it is a sunflower's swollen rhizome-tuber. Eaten raw it is crisp, sweet and faintly nutty, like a water chestnut crossed with a globe artichoke heart; roasted, fried or puréed it turns silky, creamy and chestnut-sweet, prized in autumn-and-winter cooking for soups, gratins, crisps and velvety purées.