Torta di Nocciole (Hazelnut Cake)

Unlike most versions of the classic Piedmontese hazelnut cake, this one is made without flour and is leavened solely by beaten egg whites. Usually, the cake also contains a little cocoa powder, which to me distracts from the nut taste. Serve the cake with zabaione made with Moscato or Barolo — the latter should be an old-fashioned, light-colored one or …