Preheat your oven to 350°F (175°C) and line a muffin tin with cupcake liners.
In a large bowl, mix flour, sugar, cocoa, baking soda, baking powder, and salt.
In another bowl, whisk together the egg, buttermilk, vegetable oil, and vanilla.
Add the wet ingredients to the dry ingredients and mix until just combined.
Stir in the boiling water until the batter is smooth.
Fill each cupcake liner about two-thirds full with batter.
Bake for 18-20 minutes, or until a toothpick comes out clean.
Let cool in the pan for 5 minutes, then transfer to a wire rack.
Frost with your favorite chocolate frosting once cooled.