Follow the steps in order for the best result.
Get started by preheating your oven to 350 degrees F (175 degrees C). Prepare two 9-inch cake pans by greasing them and then lightly dusting with flour. To ensure the cake doesn't stick, consider lining the bottoms of the pans with parchment paper circles. For a cleaner look, use cocoa powder instead of flour to avoid any white residue.
Now, let's create the cake batter. In a medium-sized mixing bowl, combine the sugar, flour, cocoa powder, baking soda, baking powder, and salt. Add the eggs, milk, oil, and vanilla extract. Using an electric mixer, blend these ingredients for approximately 3 minutes. Gently incorporate the boiling water by hand, stirring until just combined. The batter will be quite thin, but don't worry – that's perfectly normal!
Evenly pour the batter into the prepared cake pans. Place the pans in the preheated oven and bake for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean. Keep in mind that baking times can vary depending on your oven and even the weather.
Allow the cakes to cool in the pans for 10 minutes before carefully transferring them to a wire rack to cool completely.
While the cakes are cooling, prepare the frosting. In a large bowl, cream the butter until it's light and fluffy. Gradually add the cocoa powder and confectioners' sugar, alternating with the milk and vanilla extract. Continue to beat until the frosting reaches a smooth, spreadable consistency.
Once the cakes are completely cool, use a long serrated knife to carefully slice each layer horizontally. Spread a generous amount of frosting over the top of each layer. Stack the frosted layers on a serving plate, and then frost the entire outside of the cake.
For an extra-rich chocolate flavor, consider using Dutch-processed cocoa powder. It truly enhances the cake's deliciousness!