In a large mixing bowl, sift together the flour, cocoa powder, baking powder, and baking soda. Add the sugar and salt, then whisk briefly to combine.
Incorporate the eggs, milk, oil, and vanilla extract into the dry ingredients. Whisk thoroughly until the mixture is smooth and free of lumps, which should take about 30 seconds.
Carefully add the boiling water to the batter and whisk until fully integrated. The batter will be very thin (refer to the video for consistency).
Divide the batter evenly between the prepared cake pans.