Butter 2 pint glasses and set aside. Melt the butter in a pan then add the Guinness, sugar, cocoa powder and beat until smooth.
Mix the eggs and sour cream in a separate bowl until smooth and then whisk in the Guinness mixture. Sieve in the flour and fold in until incorporated.
Divide the mixture between 2 pint glasses and place in the pre-heated oven for 1 hour, or until a skewer inserted into the cake comes out clean. Allow to cool.
To make the icing, whisk the butter until completely softened then add ¾ of the icing sugar and whisk until incorporated. Add the irish cream and the final ¼ of icing sugar, whisking until you have smooth icing.
Ice the chocolate cakes to look like the head of a pint of guinness and enjoy!
