Preheat the oven to 350°F (175°C). Grease and flour the two 9-inch round cake pans. You may also line the bottoms with parchment paper for easy removal.
In a large mixing bowl, sift together the flour, cocoa powder, sugar, baking powder, baking soda, and salt until well combined.
Add the eggs, milk, vegetable oil, and vanilla extract to the dry ingredients. Beat on medium speed with an electric mixer for about 2 minutes until the batter is smooth and well combined.
Carefully stir in the boiling water to the batter. The batter will be thin, but this is normal. If desired, fold in the dark chocolate chips at this point.
Divide the batter evenly between the prepared cake pans.
Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Once baked, remove the cakes from the oven and allow them to cool in the pans for 10 minutes. Then, transfer the cakes to a cooling rack to cool completely.
Once the cakes are completely cool, you can frost or dust them with powdered sugar as desired before serving.
For an extra layer of flavor, consider adding a chocolate ganache or buttercream frosting.