(Source: Modified from Barefoot Contessa At Home by Ina Garten, pg. 165)
Place the flour, sugar, cocoa, baking soda, baking powder, and salt into the bowl of an electric mixer fitted with the whisk attachment and whisk together until combined. ( I like to use this method in lieu of sifting).
In another bowl, combine the buttermilk, oil, eggs, vanilla, and the Baileys Irish Cream.
Switch out the whisk for the paddle attachment and on low speed, slowly add the wet ingredients to the dry.
With mixer still on low, add the coffee and stir just to combine, scraping the bottom of the bowl with a rubber spatula.
Spoon the batter into the lined muffin tins and bake for 18 – 20 minutes, or until a cake tester comes out clean. Cool in the pans for 20 minutes, then turn them out onto a cooling rack and cool completely.