Preheat your oven to 350°F (175°C) and line a muffin tin with cupcake liners.
In a large mixing bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt.
Add the vegetable oil, milk, vanilla extract, and egg to the dry ingredients and mix until well combined.
Carefully add the boiling water to the batter and mix until smooth. The batter will be thin.
Pour the batter into the prepared muffin tin, filling each liner about two-thirds full.
Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center of a cupcake comes out clean.
Allow the cupcakes to cool in the tin for 10 minutes, then transfer to a wire rack to cool completely.