Preheat your oven to 350°F (175°C). Line a muffin pan with cupcake liners.
In a large bowl, whisk together the flour, cocoa powder, granulated sugar, brown sugar, baking powder, and baking soda.
In a separate bowl, whisk the buttermilk, vegetable oil, egg, and vanilla extract until smooth.
Combine the wet and dry ingredients, mixing until just combined.
Slowly add the hot water, stirring gently (be careful not to splash!).
Fill cupcake liners halfway with batter.
Bake for 18-20 minutes, or until a toothpick inserted in the center comes out clean.
Let cupcakes cool completely before frosting.