In a small saucepan, simmer Guinness until reduced to 1/3 cup. Pour into a medium bowl and let cool for about 10 minutes or until ready to use.

Preheat oven to 325 degrees Fahrenheit. Line a square pan with parchment paper and spray with cooking spray. Set aside.

Add oil and egg to the brownie mix and mix until well combined. Stir in brownie mix until just combined.

Reserve about 1/2 cup of brownie mix, and spread the remainder into the prepared pan.

In a small bowl, using an electric mixer, beat cream cheese until fluffy.

Beat in egg and sugar until well combined, then beat in Baileys until just combined.

Spread cream cheese mixture evenly atop brownie mix.

Use reserved brownie mix to add spoonfuls onto the cream cheese mixture, then use a table knife to swirl in a pattern.

Bake for about 50 minutes, or until brownies are still slightly wiggly but not watery.

Allow to cool in the pan for at least 30 minutes, then lift parchment paper to remove and cool completely.

Use a sharp knife to cut into squares, wiping the knife between each cut for clean slices.