Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans, and line the bottoms with parchment paper for easy removal.
In a large mixing bowl, combine the flour, sugar, cocoa powder, baking powder, baking soda, and salt. Whisk together until well combined.
In a separate bowl, whisk together the eggs, milk, vegetable oil, and vanilla extract. Pour the wet ingredients into the dry ingredients and mix until just combined. Do not overmix.
Gradually add the boiling water to the batter, stirring gently until the batter is smooth. The batter will be thin, but that is normal.
Divide the batter evenly between the prepared cake pans. Tap the pans on the counter a few times to remove any air bubbles.
Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center of the cakes comes out clean. Remove from the oven and let the cakes cool in the pans for 10 minutes before transferring them to a wire rack to cool completely.
Once the cakes have cooled, you can level the tops if necessary to ensure an even surface for frosting.