Pre heat oven 180 C /160 C fan forced. Grease a deep slice pan and line base and sides with baking paper.

Combine sugar, butter, baking soda, cocoa, and 1 cup water in a saucepan over low heat. Cook stirring for 5 minutes until sugar dissolves. Bring to the boil, reduce heat to medium and allow it to simmer or until mix doubles. Transfer to a large bowl and let it cool for 15 minutes.

Add flour and eggs. Using an electric mixer, beat mix until pale and smooth. Pour mix into pan. Bake for 35 minutes or when a skewer inserted into cake comes out clean. Stand in tin for 10 minutes and then turn out onto a cake rack to cool completely.

Frosting - Place butter, caster sugar and 2 tbsp of water in a saucepan on medium heat.Bring to the boil add icing sugar and cocoa mix till smooth and then cool in the fridge for 30 minutes till it thickens. Ice cake with frosting.