Preheat the oven to 350ºF. Line a cupcake pan with 12 liners and set aside.
To a small mixing bowl add the cocoa powder and hot coffee. Mix thoroughly until the mixture looks like a thick paste then set aside.
To a large mixing bowl, add the eggs, sugar, oil, sour cream and vanilla then whisk on a medium speed until smooth.
Add the chocolate paste to the mixing bowl and whisk on a medium speed until completely combined and uniform in color.
Tip the flour, baking powder, baking soda and salt into the mixing bowl. Use a rubber spatula to gently fold the ingredients together until just combined. Be sure to thoroughly scrape the bottom of the mixing bowl to check for any pockets of flour that might not have mixed in.
Transfer the cupcake batter to the prepared cupcake liners. The batter will be very thin, which is completely normal.
Bake in the center of the preheated oven for 18 minutes or until the cupcakes feel springy to the touch. A toothpick inserted into the middle of the cupcakes should come out clean. Remove from the oven and leave to cool for a few minutes in the pan then transfer to a wire rack to cool completely.