Preheat your oven to 350°F (175°C) and line a muffin tray with 12 cupcake liners.

In a large mixing bowl, combine the all-purpose flour, black cocoa powder, baking soda, and kosher salt. Whisk until well blended and free of lumps.

In a separate jug, whisk together the eggs, vegetable oil, buttermilk, vanilla extract, white vinegar, and granulated sugar until smooth.

Pour the wet mixture into the bowl of dry ingredients and gently fold together until just combined.

Fill each cupcake liner halfway with batter and bake for 18-20 minutes. Check for doneness with a toothpick.

Cool the cupcakes in the tray for 15 minutes before transferring them to a cooling rack.

In a stand mixer, beat the unsalted butter and confectioners' sugar on medium speed until thick and creamy, about 2 minutes.

Gradually add in the black cocoa powder, vanilla extract, and a pinch of salt, mixing until fluffy.

Gradually add the heavy cream while mixing until the frosting is light and fluffy.

Frost the completely cooled cupcakes using a piping bag.