Pre-heat the oven to 160°C/320°F and grease the baking pan. In a saucepan, heat the Guinness and chopped butter until the butter melts.
Whisk in the cocoa and sugar.
Beat the sour cream with the eggs and vanilla. Then, add this to the buttery mixture.
Whisk in the flour and baking soda. Pour the batter into the baking pan and bake for approx. 45 – 60 min. at 160°C/320°F.
Ensure the cake is cooled (approx. 2 hrs.) before it is removed from the pan and iced.
To make the frosting, lightly whip the cream cheese until it is smooth. Sift the powdered sugar into the cream cheese and beat them together. Add heavy cream and further beat to achieve a spreadable consistency. Spread the frosting on the cooled cake and serve.