Preheat your oven to 350 degrees F. Place 12 cupcakes liners into the cavities of a cupcake tin.
In a large bowl, add the flour, sugar, cocoa powder, black cocoa powder, baking soda, baking powder and salt. Mix until combined.
To the dry mixture, crack in the eggs, pour in the buttermilk, Baileys, coffee, neutral oil and vanilla extract. Mix until smooth. The batter will be thin—that’s ok!
Fill each of the cupcake liner about 1/2 way. Transfer to the oven to bake for about 18 to 20 minutes, until a skewer inserted into the center comes out clean. Allow to cool in the pan for about 5 minutes and then transfer to a cooling rack and cool until room temperature before frosting.
Repeat with the remaining cupcake batter. I got 30 cupcakes with this amount.
To Make the Vanilla Buttercream:
In the bowl of a stand-up mixer, with the paddle attachment, add the butter, powdered sugar and kosher salt; beat until smooth and fluffy, about 30 seconds. Pour in Baileys; beat until nice and fluffy, about 1 minute.