In a small bowl, blend the flour, cocoa powder, baking powder and salt.
Separate the eggs. Place the whites in a mixing bowl with 3/4 teaspoon cream of tartar. Set aside.
Put the yolks in a very large mixing bowl. Beat them with an electric beater on high speed for a few minutes until very thick and pale yellow. Add the sugar gradually and continue beating for another couple of minutes. It should be pale and very thick.
Add the dry ingredients to the yolk/sugar mixture, alternating with the cold water and vanilla (dry-wet-dry-wet-dry), beating after each addition until blended, scraping down the sides as necessary.
Beat the whites until stiff peaks hold.
Delicately fold the whites into the cake batter: begin by folding in about a third of the whites in order to lighten the heavy batter. Then fold in another third, then the final third. Don’t overdo it or, again, you will knock out too much air.
Pour into an ungreased 10-inch tube pan. Bake in the preheated oven for about 55- 60 minutes until set. If you think it is done, if the cake is risen high and seems baked through simply press the top very lightly. If you hear a foamy sound – don’t worry, if you hear or feel that foamy sensation you will know it – simply let the cake bake for another couple of minutes. If the cake is not perfectly baked through it risks falling as it cools.
Invert the cake and let cool, while the cake is still stuck to the pan. Once cooled, loosen cake from pan (I use a plastic knife) until cake slides out of pan.
The nutrition information provided are only estimates based on an online nutritional calculator. This is not a comprehensive list of all the nutrients in the recipe (i.e., does not include vitamins, cholesterol, etc). I am not a certified nutritionist. Please consult a nutritionist or doctor for accurate information and any dietary restrictions and concerns you may have.