Preheat the oven to 325 degrees. Grease and flour a 10-inch tube pan; set aside.
In a large mixing bowl, cream the butter and shortening. Gradually add 1 ½ cups of the sugar and beat until the mixture is light and fluffy. Add the egg yolks. Beat on medium high speed for 5 minutes.
In another mixing bowl, stir together the flour, salt and baking soda.
Add the flour mixture and sour cream to the butter mixture, alternately, beginning and ending with the flour mixture. Mix just until blended after each addition.
Stir in the vanilla, 1 1/3 cups of the chocolate pieces and all of the grated chocolate.
Using clean beaters and a clean medium mixing bowl beat the egg whites until foamy. Gradually add the remaining ½ cup sugar to the egg whites, beating until stiff peaks form.
Stir one third of the beaten egg white mixture into the batter to lighten it. Then, carefully fold in the remaining egg white mixture.
Spoon the batter into the prepared pan and bake for 1 hour and 20 minutes to 1 hour and 30 minutes or until a toothpick inserted near the center comes out clean. Cool in the pan for 10 minutes, then invert onto a serving plate. While the cake is still warm, spoon the glaze over it and sprinkle with the remaining chocolate chips. Cool before serving. 16 servings.
1 cup confectioners’ sugar
1 tablespoon milk
Combine the confectioners’ sugar and the milk. Add more milk if a thinner consistency is desired.