Preheat the oven to 350°F. Line a muffin pan with 12 cupcake liners and set aside.

Put the cocoa powder, instant coffee (or espresso powder) and boiling water into a small bowl and whisk until a smooth paste forms then set aside to cool.

In a large mixing bowl, add the eggs, sugar, vegetable oil, buttermilk and vanilla extract. Whisk until completely combined (1-2 minutes).

To the bowl, add the cooled chocolate paste and whisk again until completely combined.

Sift in the flour, baking soda, baking powder and salt then use a rubber spatula to gently fold the dry ingredients into the wet ingredients. The mixture will look very runny and that is fine.

Divide the cupcake batter between the cupcake liners. They will be around ¾ full.

Put the cupcakes into the center of the preheated oven and bake for 18 minutes or until the cupcakes spring back when touched with your finger and a toothpick inserted into the middle comes out clean.

Leave the cupcakes in the muffin pan for 5 minutes then transfer to a wire rack to completely cool.

In the large bowl of a stand mixer fitted with the paddle attachment (or use a large mixing bowl and handheld electric whisk) add the powdered sugar, cocoa powder and butter. Mix on the slowest speed until the butter has dispersed into the flour and cocoa powder. It will look very dry and grainy at this stage.

Keeping the mixer on the slowest speed, slowly pour in the milk. When all the milk has been incorporated turn the speed up to medium high and beat until the buttercream is light and creamy (4-5 minutes).

Transfer the buttercream into a piping bag fitted with a piping nozzle. I used a Wilton 1M.

Pipe buttercream swirls on top of each cooled cupcake then decorate with sprinkles or chocolate curls.

Serve and enjoy!