Step 1

Preheat oven to 180°C/160°C fan-forced. Grease a 3cm-deep, 17.5cm x 27cm (base) slice pan. Line base and sides with baking paper, allowing 3cm overhang at long ends.

Step 2

Combine sugar, butter, bicarbonate of soda, cocoa and 1 cup cold water in a saucepan over low heat. Cook, stirring, for 5 minutes until sugar dissolves. Bring to the boil. Reduce heat to medium. Simmer for 2 minutes or until mixture doubles. Transfer to a large bowl. Cool for 15 minutes.

Step 3

Add flour and eggs. Using an electric mixer, beat mixture until pale and smooth. Pour mixture into prepared pan.

Step 4

Bake for 35 minutes or until a skewer inserted in centre comes out clean. Stand in pan for 10 minutes. Turn, top side up, onto a wire rack to cool completely.

Step 5

Make frosting: Place butter, caster sugar and 2 tablespoons cold water in a saucepan over medium-high heat. Bring to the boil. Remove from heat. Sift icing sugar and cocoa into a bowl. Gradually add butter mixture. Stir to combine. Cover. Refrigerate for 30 minutes or until frosting thickens. Beat with a wooden spoon until spreadable. Spread cake with frosting. Serve.