- Step 1
Place chocolate and butter in a heatproof, microwave-safe bowl. Microwave on MEDIUM (50%) for 1 to 2 minutes, stirring every 30 seconds with a metal spoon, or until melted and smooth. Set aside to cool.
- Step 2
Preheat oven to 180°C/160°C fan-forced. Grease a 5.5cm-deep, 21cm x 30cm (base) baking pan. Line base with baking paper. Sift flours, bicarbonate of soda and cocoa in a large bowl. Add sugar. Stir to combine. Whisk eggs and buttermilk together in a jug. Stir buttermilk mixture, then chocolate, into flour mixture. Pour into prepared pan. Bake for 55 minutes to 1 hour or until a skewer inserted into the centre comes out clean (cover with foil if over browning). Cool in pan.
- Step 3
Make Chocolate frosting: Using an electric mixer, beat butter until light and fluffy. Gradually add icing sugar mixture, cocoa and milk, beating constantly until combined. Spread top of cake with frosting. Cut into 24 pieces. Serve.
To freeze: Refrigerate cake for 30 minutes or until frosting is firm. Wrap in plastic wrap, then foil. Freeze for up to 2 months.
To thaw: Unwrap cake. Thaw in fridge overnight. Stand at room temperature for 30 minutes before serving.