Preheat your oven to 350°F (175°C). Line a 9x13-inch baking pan with parchment paper, leaving some overhang for easy removal later.
In a large mixing bowl, combine the melted butter, light brown sugar, and granulated sugar. Whisk until the mixture is smooth and creamy. Add in the Baileys Irish Cream and vanilla extract, mixing until well combined.
Crack in the two large eggs and the additional egg yolk, making sure they are at room temperature. Whisk again until everything is well incorporated.
In a separate bowl, whisk together the all-purpose flour, baking soda, ground cinnamon, salt, and espresso powder. This will ensure that the dry ingredients are evenly distributed.
Gradually add the dry ingredient mixture to the wet ingredients, folding gently with a spatula until just combined. Be careful not to overmix; it’s okay if there are still a few flour streaks.
Gently fold in the semi-sweet chocolate chips, reserving a handful to sprinkle on top later if desired.
Pour the cookie dough into the prepared baking pan, spreading it evenly. If you reserved some chocolate chips, sprinkle them on top. Bake in the preheated oven for 25-30 minutes, or until the edges are golden brown and a toothpick inserted in the center comes out with a few moist crumbs.
Allow the cookie bars to cool in the pan for about 10 minutes before lifting them out using the parchment paper. Transfer to a wire rack to cool completely before slicing into bars. Optionally, sprinkle with flaky sea salt before serving for an added touch of flavor.
