Classic Black and White Cookie vs Mousse au Chocolat: Velvety French Chocolate Delight

Both desserts rely on butter, sugar and egg, but put them to very different work. The Black and White Cookie creams butter with sugar, adds a whole egg and baking powder, and bakes into a cookie with lightly golden edges and a set center, finished with a two-sided glaze: one half vanilla, the other darkened with cocoa powder. The mousse melts butter into dark chocolate, whisks the yolks with sugar until pale and thick, then folds in stiffly whipped whites and chills, giving an unbaked, light, airy texture and a deep dark-chocolate flavor.