Chop the chocolate finely and place in a small bowl over a pan of hot water to melt, stirring occasionally. Remove the bowl from the pan and allow the chocolate to cool slightly.
Beat the butter with half the sugar until soft and light, either by hand, with a hand mixer set at medium speed, or in a heavy-duty mixer fitted with the paddle. Beat in the chocolate, then the egg yolks, one at a time, scraping the bowl and beater(s) often. Continue beating until the mixture is smooth and light.
Place the walnuts in the bowl of a food processor fitted with the metal blade and grind them until fine, pulsing the machine on and off at 1-second intervals. Be careful that the walnuts do not become pasty. Stir the walnuts into the batter, then the flour.
In a clean, dry bowl, whip the egg whites until they hold a very soft peak, and whip in the remaining sugar in a slow stream. Whip the whites until they hold a soft, glossy -peak. Stir one-fourth of the whites into the batter, then fold in the rest with a rubber spatula so that no streaks remain. Pour the batter into the prepared pan and smooth the top. Bake the torta at 350 degrees for about 40 minutes, until the center is firm when pressed with the flat palm of your hand.
Cool the cake in the pan for 10 minutes. The cake may sink slightly, but this will not affect its texture. Trim off any loose crust and invert the cake onto a rack, remove the pan, and allow to cool completely.
Dust the cake with the confectioners’ sugar and slide onto a platter.
Confectioners’ sugar for finishing
© 1990 Nick Malgieri. All rights reserved.