Preheat your oven to 350°F (180°C). Grease two 9 inch round cake pans and line the bottoms with parchment paper.
In a large bowl, sift together the flour, cocoa powder, baking powder, and baking soda. Whisk in the sugar and salt until combined.
Add the eggs, milk, oil, and vanilla extract. Whisk well for about thirty seconds, until the batter is smooth and lump free.
Slowly whisk in the boiling water. The batter will turn very thin. That is normal.
Divide the batter evenly between the two prepared pans. Bake for 35 minutes, or until a toothpick inserted in the center comes out clean.
Let the cakes cool in the pans for 10 minutes, then turn them out onto a wire rack to cool completely.
Once fully cool, frost with chocolate buttercream frosting.