• Place 1 tablespoon lemon juice into a full sized measuring cup, fill to top with milk, set aside for 5 minutes. This will create a buttermilk substitute.
• Preheat oven to 180oC. Lightly grease a 6cm-deep, 20cm round cake pan.
• Sift flour, bicarbonate of soda and cocoa powder into a large bowl. Stir in sugar.
• Combine buttermilk substitute with eggs, melted butter and vanilla. Make a well in dry mixture and pour in the wet mixture.
• Using an electric mixer, beat on low speed to combine, then on high until mixture is thick and creamy.
• Pour mixture into prepared pan. Bake for 40 to 45 minutes or until skewer inserted into centre comes out clean. Allow to cool in pan for 5 minutes. Turn onto wire rack to cool completely.

Icing

• Sift icing sugar and cocoa powder in a bowl. Add butter and 1 tablespoon boiling water. Stir until smooth. Spread over cake. Allow icing to set then serve.