Preheat oven to 350°F and grease two 9-inch round cake pans
In a large bowl, combine sugar, flour, cocoa, baking powder, baking soda and salt and stir
Add eggs, milk, vegetable oil and vanilla extract and beat with an electric mixer on medium speed for 2 minutes. Then stir in boiling water (the batter will be thin)
Evenly pour the cake mix into the two round cake pans
Bake for 30 to 35 minutes. Once baked all of the way through, let the cakes cool for 10 minutes before removing the cakes from the pans and placing on a wire rack
Chocolate Frosting
In a microwave safe bowl, melt the butter
In a large bowl, combine melted butter and cocoa. Alternately add powdered sugar and milk to a spreading consistency
If the frosting is too thick to spread with a butter knife, add a small splash of milk until the desired consistency is reached