For the brownies:

1. Preheat the oven to 350°F.
2. Place parchment paper in the bottom of an 8×8 baking pan, leaving the parchment to hang over 2 sides of the dish. This will make the brownies easy to remove once they are baked.
3. Brush the parchment with a little bit of butter.
4. In a medium saucepan, bring 1 cup of Guinness to a boil. Boil until the liquid reduces by half, watching to make sure the stout doesn’t bubble too much.
5. Stir the butter into the reduced Guinness until melted.
6. Add sugar and whisk until dissolved.
7. Whisk in the salt and cocoa until smooth.
8. Remove from the heat and let cool until just warm.
9. Once cooled, stir in the eggs, vanilla extract, and then stir in the flour until smooth.
10. Gently incorporate the chopped chocolates and walnuts.
11. Pour into the prepared baking pan, and bake at 350°F for 30-35 minutes.
12. Let the brownies cool completely before icing.

For the icing:

1. With an electric mixer on medium speed, beat the softened butter until soft and creamy.
2. Gradually add in the powdered sugar, 1 cup at a time, occasionally scraping down the sides of the bowl with a spatula.
3. Once the sugar is completely incorporated, add the Baileys and the heavy cream.
4. Spread the icing over the completely cooled brownies, or pipe the icing on individual brownie squares. Add sprinkles as desired.