Preheat the oven to 350?F (175?C) and line a muffin tin with cupcake liners.

In a mixing bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt.

In another bowl, beat the softened butter until creamy. Add the eggs, Baileys, and milk, and mix until well combined.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Fill each cupcake liner about 2/3 full with batter.

Bake for 18-20 minutes or until a toothpick inserted into the center comes out clean. Let cool completely.

In a mixing bowl, beat the softened butter until creamy.

Add the cocoa powder and mix until combined.

Gradually add the powdered sugar, alternating with Baileys, until the desired consistency is reached.

Mix in the vanilla extract.

Once the cupcakes are completely cool, frost them generously with the chocolate frosting.

Optional: Decorate with chocolate shavings or sprinkles.