Preheat oven to 350 degrees. Grease a 9×9 square baking pan and line it with parchment paper.
Mix together the oil, guinness, sugar and vanilla extract in a large bowl.
Add butter and mix until well combined.
Add eggs and mix until well combined.
Combine flour and cocoa in another medium sized bowl.
Slowly add dry ingredients to the egg mixture until well combined.
Pour the batter into the pan and spread evenly.
Bake for 35-38 minutes, or until a toothpick comes out with a few crumbs. Allow brownies to cool.
To make ganache, place chocolate chips, butter and guinness into a microwave safe bowl and microwave until guinness gets hot and butter starts to melt.
Whisk together chocolate mixture until smooth, microwaving for a little longer, if needed, using 30 second increments.
Add powdered sugar and whisk until smooth.
Pour ganache over brownies and spread into an even layer.