Bring the Guinness to a boil in a small saucepan and then reduce to a simmer for 5 to 10 minutes while stirring occasionally.  You’re aiming to reduce it to about a 3/4 cup.  Remove from the heat, measure out a 1/2 cup for the cake portion and set the remainder aside for the frosting.  Leave both to cool to room temperature.

Preheat the oven to 350, spray a 9 x 9 baking pan, line it with parchment leaving an overhang on 2 sides (if you wish, for easy removal) and spray the parchment.  Place the butter and chocolate into a large microwaveable bowl and then heat/melt in 30 second increments until the butter and chocolate can be whisked together smoothly.  Whisk in the sugar and the cooled 1/2 cup of reduced Guinness, then whisk in the eggs and vanilla. Lastly whisk in the flour, salt and espresso powder.  Scrape the batter into your prepared pan, smooth the top and then bake for about 30 minutes until the center temperature reaches 200.  Remove from the oven and leave on a wire rack to cool completely before frosting.

For the frosting, use your mixer to beat the butter for a couple of minutes until smooth and fluffy then add in the icing sugar and mix on low until it gets worked in a bit.  Increase the speed and drizzle in a couple of tablespoons of reduced Guinness, then the espresso powder, vanilla and salt.  Scrape down the sides and beat again.  You’ll likely need to add a titch more Guinness – if you’ve run out then use room temperature cream or milk.  Beat again and add liquid as needed until you have a spreadable consistency that works for you.  Ice as you wish and serve up the Guinness Brownies! – these are rich so if there’s any left over they’ll be equally fudgy and delicious the next day.