These cookies get their pleasing texture (and their descriptive name) by mixing the flour with the cocoa powder and sugar and then working in the pieces of butter until the mixture resembles coarse sand. (In contrast, many other cookie doughs have you cream the butter with the sugar until completely smooth.) The dough is quickly rolled into balls with your hands, then flattened before baking. The ganache topping can be made with any type of chocolate, or all three for a variet.