Preheat oven to 350 F. Grease & flour either 2- 9inch round cake pans or a 13x9 or I used a 3 qt. baking dish in this picture and set aside. In a medium bowl whisk together the cocoa and boiling water until smooth. Cool this mixture to room temperature.
In another bowl lightly combine the eggs, 1/4 of the cocoa mixture, and vanilla. In a large mixing bowl combine the remaining dry ingredients and mix on low speed for about 30 seconds until combined. Add the butter and remaining cocoa mixture.
Mix on low speed until the dry ingredients are moistened. Increase to medium speed and beat 1 1/2 minutes to develop cakes structure. Scrape the sides, then add the egg mixture in 3 batches, beat 20 seconds after each addition to mix ingredients together. Scrape down the sides again.
Scrape batter into prepared pans, pan or dish and smooth the surface evenly with a spatula. The pan will be 1/2 full. Bake 25-35 minutes or until cake tests done in center with a toothpick. Let cake cool 10 minutes in pan. Then remove to a wire rack to cool completely. Frost or leave plain.