Preheat the oven to 350°F (180°C) and line a cupcake tray with 12 cupcake liners.
Sift the all purpose flour and cocoa powder into a mixing bowl and add the sugar, baking soda, baking powder, salt and instant espresso powder and mix together.
Prepare the homemade buttermilk by adding ½ tablespoon of lemon juice to a measuring jug and then adding milk (room temperature) up to the ½ cup (120ml) line. Let it sit for a minute to curdle.
Add the homemade buttermilk, oil, egg and vanilla to the mixing bowl and mix in to a thick batter.
Add the hot water and use a hand whisk to whisk it in until well mixed. Your batter will now be thin and this is perfect.
Divide the batter between the 12 cupcake liners.
Place into the oven to bake for 20 minutes or until a toothpick inserted into the center of one of the cupcakes comes out clean (no wet batter).
Transfer to a wire cooling rack to cool completely before frosting.