Preheat oven to 350°F (175°C) and grease an 8 × 8 inch baking pan with cooking spray.
In a large bowl, whisk together brownie mix, Guinness, vegetable oil, and egg until well combined.
Spread the brownie batter evenly into the prepared baking pan.
Bake according to package directions or until a toothpick inserted in the center comes out with a few moist crumbs, about 35 minutes.
Allow the brownies to cool completely in the pan.
Place the chocolate chips in a medium heatproof bowl to prepare the ganache.
In a small saucepan over medium heat, bring the heavy cream and Guinness just to a boil.
Pour the hot cream mixture over the chocolate chips, ensuring they are fully submerged.
Let the mixture sit for about 30 seconds, then whisk until smooth and glossy.
Pour the ganache over the cooled brownies and spread it evenly.
Refrigerate the brownies for about 15 minutes or until the ganache is set.
Slice into squares and serve.
