01 - Preheat oven to 350°F. Grease and flour two 9-inch round cake pans, tapping out any excess flour.
02 - In a large mixing bowl, whisk together the all-purpose flour, cocoa powder, granulated sugar, baking powder, baking soda, and salt until evenly distributed.
03 - Add the eggs, whole milk, vegetable oil, and vanilla extract to the dry mixture. Beat until the batter is smooth and no lumps remain.
04 - Gradually pour in the boiling water while mixing on low speed. Continue until fully combined. The batter will be noticeably thin — this is normal.
05 - Pour the batter evenly between the two prepared cake pans, smoothing the tops with a rubber spatula.
06 - Bake for 30 to 35 minutes, or until a toothpick inserted into the center of each layer comes out clean. Avoid overbaking to retain moisture.
07 - Let the cakes rest in their pans for 10 minutes, then invert onto wire racks to cool completely before frosting.
08 - Beat the softened butter with an electric mixer until light and creamy. Gradually add powdered sugar and cocoa powder, mixing on low. Pour in the milk and vanilla, then increase speed and beat until the frosting is smooth and fluffy.
09 - Place one cooled layer on a serving plate. Spread a generous layer of frosting over the top. Position the second layer on top, then frost the sides and top of the entire cake evenly.