In a large mixing bowl, whisk together sugar, flour, cocoa, baking powder, baking soda and salt. Mix thoroughly. Use the whisk attachment if using your electric mixer.
In a separate smaller bowl, mix together eggs, milk, oil and vanilla. Pour liquid mixture into dry ingredients.
Whisk for 2 minutes.
Carefully, stir in boiling water. (Batter will be very thin)
Pour fully mixes batter into prepared muffin tins.
Bake for 20 minutes or until fully cooked.
Allow to cool in the pan for 10 minutes and then carefully move the cupcakes to finish cooling on a rack.