Preheat oven to 180C and line a cupcake pan with paper liners.
In a mixing bowl, whisk together the sugar, oil, egg, and vanilla essence well.
Add the flour, cocoa powder, baking soda, and salt. Mix together until combined.
Mix in the hot water, ⅓ at a time. The batter will be thin in consistency.
Pour batter into prepared cupcake pan, filling each paper liner ⅔ of the way full.
Bake for 15 minutes, or until the centres have puffed up and a toothpick comes out clean.
Allow the cupcakes to cool in the tin for 10-15 minutes, then transfer to a cooling rack.