Preheat the oven to 350°F (180°C) and grease a 9x13 inch baking pan.
In a large mixing bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt.
Add the eggs, milk, vegetable oil, and vanilla extract to the dry ingredients, and mix until well combined.
Gradually pour in the boiling water and stir until the batter is smooth and well combined.
Pour the batter into the prepared baking pan and bake for 30-35 minutes, or until a toothpick inserted into the center of the cake comes out clean.
Remove the cake from the oven and allow it to cool in the pan for 10 minutes.
Use a knife to loosen the edges of the cake from the pan, and then invert it onto a wire rack to cool completely.
Dust the top of the cake with powdered sugar (optional) and serve.