Chocolate Cinnamon Angel Food Cake

1 1/2 cups egg whites (10-12 eggs)
1 cup sifted all-purpose flour
1 1/2 cups sifted confectioners' sugar
3 tablespoons unsweetened cocoa
1/2 teaspoon cinnamon
1 1/2 teaspoons cream of tartar
1 teaspoon vanilla extract
1 cup granulated sugar

Bring egg whites to room temperature, about 1 hour.

Meanwhile, sift flour, cocoa, confectioners' sugar and cinnamon together three times. Set aside.

In a large mixer bowl, beat the egg whites, cream of tartar and vanilla extract with an electric mixer on medium speed until soft peaks form. Gradually add the sugar, 2 tablespoons at a time, beating on high speed until stiff peaks form. Transfer to a larger bowl if needed.

Sift about one-fourth of the flour mixture over the beaten egg whites. Fold in gently. Repeat, folding in the remaining flour mixture in fourths.

Pour into ungreased 10-inch tube pan. Bake on the lowest rack in the oven at 350 degrees F for 40-45 minutes or until the top springs back when touched.

Immediately invert cake (leave in pan); cool thoroughly. Loosen sides of cake from pan; remove.

Makes 16 slices.