Preheat the oven to 180˚C (160˚C fan oven, 350˚F, Gas Mark 4). Grease and line a deep 20cm (8inch) round cake tin. Put the butter and Guinness® in a saucepan and heat very gently, without boiling, until melted. Remove from the heat and cool for 10 minutes.

Sieve the flour, Cocoa Powder and Bicarbonate of Soda into a bowl. Stir in the sugar and Chocolate pieces. Make a well in the centre. 

Mix the egg, milk and Vanilla Extract together and pour into the dry ingredients along with the Guinness® mixture. Mix well to form a smooth, thick batter.

Pour into the prepared tin and bake in the oven for about 55 minutes until risen and just firm to the touch – a skewer inserted into the centre of the cake should come out clean. Cool for 10 minutes then turn on to a wire rack to cool completely.

Pop the butter and icing sugar into a large bowl and beat together using an electric hand whisk or freestanding mixer with the beater attachment, until smooth and combined – make sure there are no lumps of butter. Pop in the Vanilla Extract and cream cheese and beat together until you have a lovely light and fluffy buttercream. 

To decorate, spread the Cream Cheese Style Icing thickly on top of the cake. Smooth the edge by drawing a palette knife around the top to make the icing in-line with the side of the cake, like the head on a pint of Guinness®. Your cake is now ready to serve and enjoy!