Preheat oven to 375°F (350F if you don't want domed cupcakes).
Line a cupcake tray with liners and set aside.
Stir sugar with flour, cocoa, baking powder, baking soda and salt in a large bowl.
Add eggs, milk, oil and vanilla, and beat well.
Slowly stir in boiling water until you reach a runny consistency.
Portion out into cupcake liners - filling 3/4 of the way through.
Bake for 18-22 minutes and allow to cool in the pan for one minute before removing to a cooling rack.