Preheat the oven to 350 degrees F. Place the cupcake liners in the muffin pan. Set aside.
In a medium bowl, combine the all-purpose flour, sugar, cocoa powder, baking powder, baking soda, and salt.
In another bowl, whisk egg, buttermilk, oil, and vanilla extract. Whisk vigorously until everything is well combined.
Add flour mixture to wet batter in batches until everything is well incorporated without any lumps.
Stir in the hot water and just combine the batter without over-mixing it.
Using an ice cream scoop, spoon the batter equally into 12 muffin liners about 2/3rd full. Bake chocolate cupcakes for 20-22 minutes until the toothpick inserted in the center comes out clean.
Place the cupcakes on a wire rack and allow them to rest until cool before frosting.