Preheat oven to 350°F. Line a 20cmx20cm (9x9inch) pan with baking paper. Set aside.

In a small saucepan, bring the Guinness to a boil. Boil for 5-10 minutes, until reduced by half. Set aside to cool slightly.

In the microwave or a double boiler, melt the chocolate chips and butter until completely smooth. Set aside to cool slightly.

In a large bowl, whisk the sugar, eggs, and vanilla extract. Add melted chocolate mixture and whisk to combine. Add the Guinness and whisk to combine. Stir in flour and salt. Pour into the prepared pan.

Bake in a pre-heated oven at 175°C – 350°F for approximately 30-35 minutes, until a toothpick inserted into the centre comes out without batter on it (a few fudgy crumbs are ok).

Cool completely, then cut into 12 squares.

Using a hand mixer or stand mixer, beat the butter and powdered sugar until combined. Add the Irish cream and vanilla. Beat on medium speed for a minute or two, until smooth and creamy.

Spread frosting over the top of the brownies, or use a piping bag and decorating tip to frost each brownie individually.