Step 1 Heat the oven to 350 degrees. Grease and flour three 9-inch round cake pans.
Step 2 Place the cocoa in a small mixing bowl and pour 2 cups boiling water over it. Stir well with a fork until smooth, and set aside to cool.
Step 3Put the flour, baking soda, baking powder and salt in a medium bowl and stir with a fork to mix well. Set aside.
Step 4With a mixer, beat the butter and sugar at high speed until well combined. Add the vanilla and then the eggs, one at a time, beating well after each until the mixture is smooth and light.
Step 5Add the flour mixture in four batches, beating after each addition only until the flour disappears. Alternate with the cocoa mixture in three batches, beating after each just enough to combine everything into a smooth, luscious batter, stopping once or twice to scrape down the sides of the bowl.
Step 6Divide the batter among the three cake pans. Bake until the cakes spring back when touched lightly in the center and are beginning to pull away from the sides of the pans, 25 to 30 minutes.
Step 7Place the cake pans on wire racks and cool the cake layers for 10 minutes. Then gently turn them out onto wire racks to cool completely, top side up.