Preheat oven to 350°F (175°C). Grease and flour an 8x8 inch baking pan.
In a double boiler or microwave-safe bowl, melt the butter and chopped semisweet chocolate together until smooth. Stir well.
In a large bowl, whisk together the granulated sugar and eggs until well combined. Stir in the vanilla extract.
Gradually whisk the melted chocolate mixture into the sugar and egg mixture until smooth.
In a separate small bowl, whisk together the flour, cocoa powder, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.
Stir in the Baileys Irish Cream until fully incorporated.
Pour the batter into the prepared baking pan and spread evenly.
Bake for 30-35 minutes, or until a toothpick inserted into the center comes out with moist crumbs attached.
Let the brownies cool completely in the pan.
For the glaze (optional): Whisk together the powdered sugar and Baileys Irish Cream until smooth. Drizzle over the cooled brownies.
Cut into squares and serve.
Notes
For an extra boozy kick, you can add an extra tablespoon of Baileys to the brownie batter. Ensure the brownies are fully cooled before glazing for best results.