Preheat your oven to 350°F (175°C). Grease and flour the 9-inch round cake pan.
In a large mixing bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt until combined.
Add the eggs, milk, vegetable oil, and vanilla extract to the dry ingredients. Beat the mixture on medium speed with an electric mixer for about 2 minutes until the batter is smooth.
Carefully stir in the boiling water. The batter will be thin, but this is normal.
Pour the batter evenly into the prepared cake pan.
Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted in the center comes out clean.
Once baked, remove the cake from the oven and allow it to cool in the pan for about 10 minutes. Then, transfer the cake to a wire rack to cool completely.
If desired, frost with chocolate frosting once cooled, and serve.