12 large egg whites

3/4 cup cake flour  (not self-rising)

1 teaspoon vanilla extract

1 teaspoon cream of tartar

1-1/4 cups sugar

1/4 teaspoon salt

1/4 cup cocoa powder

1/4 cup chocolate syrup

Preheat oven to 325 degrees. Beat egg whites in a large bowl for a few minutes before adding the cream of tartar. Beat until egg whites stand in stiff peaks. Combine the sugar and salt (if using granulated sugar, instead of superfine bar sugar, sift it twice). Slowly add the sugar to the beaten egg whites and also add the vanilla. Continue beating until peaks are not only stiff but shiny. Sift the flour and the cocoa powder together and fold into the mixture (try to deflate the egg whites as little as possible).

Spoon into an ungreased angel food cake tin. While doing this be sure there are no air bubbles and push the mixture into the sides around the tin. When about 1/3 full, drizzle the chocolate sauce over the surface. Using a spoon or spatula, plunge about 3 times into the batter for a marbled effect. Add 1/3 more batter and repeat step, plunging in different areas than last time. Now add the remainder of the batter. Keep in mind that the syrup will settle to the bottom of the tin during baking if you use too much or it is all in one area.

Put in oven on a middle or lower rack (so it doesn't brown too quickly) and bake for 50 to 60 minutes. Remove from the oven and turn upside down, using the small feet on the rim of the tin. Place on the counter to cool. It is important to have the cake upside down, otherwise it will be heavy. If your tin does not have feet, use a narrow-neck bottle to fit through the hole of the center of the pan. Let it stay until completely cooled. Run a serrated knife around the inside and outside of the tin to loosen. Also do the same around the bottom of the tin once it has been removed from the sides. Serve slices using a serrated knife in a sawing motion.

from about.com