½ cup sifted cake flour
½ cup cocoa
1 ½ cups sugar
1 tbs very finely ground coffee
½ tsp salt
12 large egg whites (cold)
1 tbs water
1 tbs fresh-squeezed lemon juice
1 tsp cream of tartar
1 tsp vanilla
Sift together flour, cocoa, ¾ cup of the sugar, coffee and salt 3 times. In a very large bowl, using an electric mixer on low, beat together egg whites, water, lemon juice, cream of tartar and vanilla for one minute. Increase the mixer speed to medium and continue beating until the mixture is about 5 times the volume and foamy (about 1 ½ to 3 minutes). Gradually beat in, one tbs at a time, the remaining ¾ cup of sugar. Do not beat stiff, but rather until soft peaks form that bend over at the tips.
Sift the flour/cocoa mixture, about ½ cup at a time, over the egg whites, gently folding it together, until it’s all been added and there are no pockets of the dry ingredients visible. Scrape batter into an ungreased 9 or 10-inch Angel Food pan with a removable bottom and level with a spatula. Bake at 350F for about 35 minutes, until a tester inserted in the centre comes out clean. Invert pan to cool for at least 1 ½ hours by setting the centre tube over the neck of a wine bottle or balancing pan edges on four glasses.
To remove from pan, slide a knife with a thin blade around the pan edges. Gently remove the outer piece of the pan and remove the cake from the tube section. Let cake cool completely on a rack.