Preheat your oven to 350°F/175°C and place 12 cupcake liners in your muffin tray.
In a large bowl, whisk together the flour, black cocoa powder, baking soda and salt. Set aside.
In a large jug, whisk the eggs, oil, buttermilk, vanilla, vinegar and sugar until smooth
Pour the wet mixture into the flour, stirring until it is just about smooth - we don't want to over mix the batter!
Fill the cupcake liners half of the way and bake for 18-20 minutes. A toothpick inserted should come out clean.
Allow the cupcakes to cool for 15 minutes in the tray, then take them out and place on a cooling rack. Bake the last two cupcakes.
Make Frosting
In a stand mixer fitted with the paddle attachment, beat the butter and confectioners' sugar together on low speed until well combined.
Increase the speed to medium-high and beat for a 2 minutes until it becomes very thick.
Stop the mixer and add the salt, vanilla, and cocoa powder into the bowl. Begin by beating slowly, then increase to medium-high speed for another 2 minutes
Turn the mixer to your lowest speed and pour in the heavy cream. Beat until it becomes very creamy and spreadable.
I used a Wilton 1M piping tip to frost my cupcakes.
Notes
My recipes have been developed and tested in metric grams. I highly recommend using a weighing scale and measuring out your ingredients the metric way. I have provided a conversion to US cups but please note that I haven't tested the recipe with this method.UPDATED RECIPE: Please note that I have updated this recipe as of April 2023! Changes have been made including removing baking powder and light brown sugar, as well as slightly decreasing the amount of vinegar and black cocoa powder. Also please note, due to the black cocoa powder these cupcakes are not overly sweet! Room Temperature: I make sure that all of my ingredients are at room temperature before I start the recipe, so pull out all of the ingredients before you start baking. Butter: I use European style butter, like Kerry Gold, in my recipes. This will make your frosting much creamier and richer.Salt: If you don't have kosher salt, halve the amount of salt called for in the recipe. 1 teaspoon kosher salt = ½ teaspoon fine salt.Cocoa Powder: I'm using black cocoa powder in this recipe. I recommend the brands De Zaan, King Arthur, or Van Houten. If you don't have black cocoa powder then you can substitute an equal amount of dutch-process cocoa powder, but please note that it won't be as dark. Storage: Store the cupcakes in the fridge for up to 5 days. Let them sit at room temperature for 30 minutes before eating.