To make these Baileys St. Patrick's Day Cupcakes, start by preheating your oven to 375 degrees and line your cupcakes tins with paper liners.
Add dark chocolate cocoa, sugar, flour, baking powder, baking soda, salt and espresso powder to a large bowl and whisk together to combine your ingredients. Next, add in the eggs, vegetable oil, vanilla and Baileys Irish cream. Using an electric mixer, mix well to combine. Finally, add in your boiling water (two minutes in the microwave is close enough!) and mix well. Your batter will be extremely thin and that is what you want.
Using a large spoon or a small measuring cup, fill your paper cupcake liners a bit over half way up with your batter and then bake for 20 minutes. Remove from the oven and the cupcake pan and move your Baileys St. Patrick's Day Cupcakes to a wire rack to cool.
Once complete cooled, add softened butter, sifted powedered sugar, salt, vanilla and Baileys to a large mixing bowl and mix well until you reach the buttercream frosting consistancy you are looking for. Either frost your cupcakes by hand or move the Baileys buttercream frosting to a large piping bag / zip top bag and frost using a decorating tip. Serve immediately and leftovers can be kept in the refrigerator.