8 ounces (1 2/3 cups) blanched almonds
7 (1 ounce) squares unsweetened chocolate
1/2 pound (2 sticks) sweet butter
1 cup plus 1 tablespoon granulated sugar
4 large eggs, separated
Confectioners' sugar, optional
Adjust rack one-third up from the bottom of the oven, and preheat oven to 300 degrees F. Butter an 8- or 8 1/2-inch springform pan that is 2 or 2 1/2 inches high. Line the bottom with a round of baking pan liner or wax paper cut to fit, and butter the paper. (It is not necessary to flour or crumb the paper or the pan.) Set aside.
The almonds and the chocolate must be ground together to a fine powder. This may be done in a food processor, blender or nut grinder. If using a processor, chop the chocolate coarsely by hand first and then place all of the nuts and the chocolate in the processor bowl fitted with the steel blade and grind until the mixture is fine. If you use a blender, chop the chocolate coarsely by hand first and then grind the nuts and chocolate together, but only part of the time. Set the ground mixture aside.
In the large bowl of an electric mixer cream the butter. Add the sugar and beat to mix. Add the egg yolks all at once and beat to mix. Then add the ground nut and chocolate mixture and beat on low speed to mix. Remove from the mixer and set aside.
In small bowl of the electric mixer with clean beaters beat the egg whites until they hold a rather firm shape, but not until they are stiff or dry. The chocolate mixture will be stiff. Stir about one-quarter of the beaten whites into it, and then fold in the remaining whites. Turn into the prepared pan and smooth the top. Bake for 45 minutes.
Let the cake cool in the pan until it is tepid or until it reaches room temperature. Remove the sides of the springform pan. Then cover the cake with anything flat and invert. Remove the bottom of the pan and the paper lining.
Cover the bottom of the cake with another flat cake plate or a serving board and very gently and carefully invert again, leaving the cake right side up. Let stand at room temperature.
The top may be sprinkled with confectioners' sugar.
Serve with vanilla ice cream.