Preheat oven to 350°F (176°C) and line baking sheets with parchment paper.
In a large bowl, cream together the butter, brown sugar, and sugar until light and fluffy.
Add the egg, Baileys Irish Cream, and vanilla extract, and mix until well combined.
In a separate bowl, whisk together the flour, cocoa powder, baking soda, and salt.
Gradually add the dry ingredients to the wet ingredients and mix until combined.
Fold in the chocolate chips.
Scoop tablespoons of dough onto the prepared baking sheets, spacing them about 2 inches apart.
Bake for 8-10 minutes or until the cookies are set around the edges but still soft in the center.
Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.