Piloncillo, unrefined whole-cane sugar, is the key ingredient of these richly nuanced cookies. Known as piloncillo in Mexico; chancaca in Chile, Bolivia and Peru; or panela in other Latin American countries, it is commonly used in both sweet and savory dishes and is made by crushing, extracting and boiling down the juice from sugar cane to caramelize the sugars. It adds notes of caramel, butterscotch and molasses to everything from cakes to barbecue sauce. In this cookie, the grated piloncillo complements the bittersweet chocolate and adds the nutty flavor of the toasted milk solids in browned butter, but without any of the work. It is a bit of a chore to grate, but the flavor it adds is well worth it.