01 - Preheat oven to 350°F. Grease and flour two 9-inch round cake pans.
02 - In a large bowl, sift together the flour, cocoa powder, sugar, baking powder, baking soda, and salt.
03 - Add the eggs, milk, oil, and vanilla extract to the dry mixture. Beat on medium speed for 2 minutes until smooth.
04 - Pour in the boiling water and mix until combined. The batter will be thin.
05 - Divide the batter evenly between the two prepared cake pans.
06 - Bake for 30–35 minutes, or until a toothpick inserted into the center comes out clean.
07 - Let cakes cool in the pans for 10 minutes, then turn out onto wire racks to cool completely.
08 - Beat butter until creamy. Sift in powdered sugar and cocoa powder, then add milk and vanilla. Beat until fluffy.
09 - Spread frosting between the cake layers and over the top and sides.