Heat oven to 350 degrees. Sift flour into a mixing bowl, then resift flour with 3/4 cup sugar. In a clean metal bowl, beat egg whites with an electric mixer until frothy. Add cream of tartar; beat until whites have tripled in size, about 3 minutes. Slowly add remaining sugar; beat 1 to 2 minutes, or until firm and glossy. Transfer egg whites to a large metal mixing bowl. Gently fold in flour mixture in three additions, mixing from bottom of bowl (try to use fewest strokes possible.) Fold in grated chocolate, and mix. Pour batter into a 10-inch non-stick angel food cake pan, and run a knife through cenbter of the batter to release any air bubbles. Bake for 40 to 45 minutes, until top becomes golden brown. Invert the pan over the neck of a bottle and cool about 1 hour. Loosen the cake from the pan with a flexible knife, and turn the cake over onto cake stand. Make ganache by heating buttermilk over medium heat; add chopped chocolate, and stir slowly until melted. Since buttermilk will curdle slightly, strain mixture through a very fine sieve, and stir slowly until smooth. Spread ganache over top of cooled angel food cake and allow to harden slightly before serving. Makes one 10 inch cake. Cuisine: "Mexican" Source: "Martha Stewart Living Magazine, Feb 1997" S(Formatted for MC5): "by Lynn Thomas - Lynn_Thomas@prodigy.net" Yield: "1 ten-inch cake" Per serving: 1794 Calories (kcal); 113g Total Fat; (50% calories from fat); 81g Protein; 171g Carbohydrate; 0mg Cholesterol; 800mg Sodium Food Exchanges: 11 Grain(Starch); 7 1/2 Lean Meat; 0 Vegetable; 0 Fruit; 22 Fat; 0 Other Carbohydrates Recipe by: Martha Stewart Converted by MM_Buster v2.0n.