Preheat your oven to 170 degrees (fan forced) and line the base of a loaf tin.
Melt the butter in the microwave and set aside to cool slightly.
Sift flour and cocoa into the bowl of an electric mixer, then add all the other ingredients.
Beat for approximately 4 minutes until ingredients have all combined and the mixture is smooth.
Pour into the cake tin and bake for 35 minutes or until a skewer inserted in the middle comes out clean.
Allow cake to cool in the tin for five minutes before transferring to a wire rack to cool completely.
Place Cocoa, Icing Mixture and Butter/Marg into a small bowl
Start by adding 2 tablespoons of boiling water to bowl and mixing together using a spoon
Continue to add water until desired consistency is achieved - icing should still be thick enough to easily spread over cake without running everywhere