Preheat the oven to 170°C/gas mark 3, then line the base of a 23cm (9in) diameter spring-form cake tin with baking parchment.

Pour the Guinness into a saucepan, add the butter and gently heat until it has melted. Remove the pan from the heat and stir the cocoa powder and sugar into the warm liquid.

Mix together the eggs, vanilla essence and milk by hand in a jug or bowl, and then add this to the mixture in the pan.

Sift together the remaining sponge ingredients into a large bowl and mix well until all the ingredients are incorporated.

Pour the batter into the prepared cake tin and bake for approximately 60 minutes or until the sponge bounces back when lightly pressed and a skewer inserted into the middle of the cake comes out clean.

Set aside to cool, and then remove from the tin on to a wire rack, making sure the cake is cold to the touch before you ice it. leaving it to rest overnight is best.

For the icing

Break the chocolate into small pieces.

Heat the rice milk in a small pan until boiling and stir in the chocolate until it has melted.

Remove from the heat and whisk in the sieved icing sugar..

Set aside to cool before spreading on the cake.