01 - Preheat oven to 350°F (175°C). Grease and flour two 9-inch round cake pans, ensuring even coverage to prevent sticking.
02 - In a large mixing bowl, sift together the all-purpose flour, cocoa powder, granulated sugar, baking powder, baking soda, and salt until well blended and free of lumps.
03 - Add the room-temperature eggs, whole milk, vegetable oil, and vanilla extract to the dry mixture. Beat on medium speed for 2 minutes until the batter is smooth and homogeneous.
04 - Pour in the boiling water and stir gently until fully combined. The batter will appear thin—this is expected and ensures a moist finished cake.
05 - Divide the batter evenly between the two prepared cake pans. Bake for 30 to 35 minutes, or until a toothpick inserted into the center of each layer comes out clean.
06 - Allow the cakes to cool in their pans for 10 minutes, then invert onto wire racks to cool completely before frosting.
07 - Beat the softened butter until light and creamy. Sift in the powdered sugar and cocoa powder, then add the milk and vanilla extract. Beat on medium-high speed until the frosting is fluffy and spreadable.
08 - Place one cooled cake layer on a serving plate. Spread an even layer of frosting over the top, then position the second layer on top. Frost the top and sides of the assembled cake using smooth, even strokes.