Preheat your oven to 350°F (175°C). Grease the two 9-inch round cake pans and line them with parchment paper.
In a large mixing bowl, sift together the flour, granulated sugar, cocoa powder, baking powder, baking soda, and salt.
Add the eggs, milk, vegetable oil, and vanilla extract into the dry ingredients. Beat the mixture on medium speed until well combined, about 2 minutes.
Gradually stir in the boiling water into the batter (the batter will be thin). Mix well until smooth.
If using, fold in the dark chocolate chips for extra chocolaty goodness.
Divide the batter evenly between the two prepared cake pans.
Bake in the preheated oven for 30 to 35 minutes, or until a toothpick inserted into the center of the cakes comes out clean.
Once baked, remove the cakes from the oven and let them cool in the pans for about 10 minutes. Then, transfer the cakes onto a cooling rack to cool completely.
Once cooled, you can frost or layer as desired, or simply dust with powdered sugar before serving.