Preheat the oven to 350°.
Grease and flour two 9-inch round cake pans, or use a baking spray.
With a mixer on low speed, mix together the sugar, flour, unsweetened cocoa powder, baking powder, baking soda, and salt.
Add the eggs, milk, vegetable oil, and vanilla extract and beat on medium speed for 2 minutes.
By hand or carefully on low speed, mix in the boiling water. The batter will be thin.
Pour into the prepared pans and bake at 350° for 25-30 minutes or until a cake tester comes out clean.
Put the pans on a wire rack to cool for 10 minutes.
Invert the cakes onto the wire rack to continue cooling.
Frost, if desired.
Store the cake covered at room temperature.