Chocolate Angel Food Cake

1 cup sifted cake flour
1 ¼ cups granulated sugar
1/3 cup unsweetened cocoa powder
¾ teaspoon ground cinnamon
½ teaspoon salt
1 ½ cups egg whites (about 12 large eggs)
1 ½ teaspoons cream of tartar
2 teaspoons vanilla extract
2 Tablespoons sifted confectioner’s sugar (optional)

Preheat the oven to 325 degrees. In a medium bowl, sift together the flour, ¾ cup of the granulated sugar, the cocoa, cinnamon and salt. In a perfectly clean large bowl, beat the egg whites with an electric mixer set on high speed until foamy. Add the cream of tartar and beat until soft peaks form. Gradually add ¼ cup of the remaining sugar in a steady stream and continue beating until the whites are stiff and glossy but not dry. Beat in the vanilla. Sprinkle the remaining ¼ cup of sugar over the top of the whites and fold in gently. Gently fold in the flour mixture. Spoon the batter into an ungreased 10-inch tube pan and bake for 45 minutes or until a toothpick inserted in the center comes out clean. Invert the pan and let cool. Transfer the cake to a serving platter and dust with the confectioner’s sugar.