1. Pre heat oven to 180 degrees celsius. Lightly grease a 20cm round cake pan. Line the base with baking paper. 2. Sift flour, bicarbonate soda and cocoa powder in a big bowl. Stir in the sugar. Combine buttermilk, eggs, melted butter and vanilla in a jug. 3. Make a well in the centre of the flour mixture. Pour in buttermilk mixture. 4. Using an electric mixer, beat on low speed until combined. Increase speed to high and beat for 3 to 4 minutes until thick and creamy. 5. Pour mixture into prepared pan. Bake for 40 to 45 minutes or until a skewer comes out clean. Cool in pan for 5 minutes. Cool on a wire rack completely. 6. To make the chocolate icing, sift the icing sugar and cocoa powder in a bowl. Add butter and 1 tablespoon of boiling water. Stir until smooth. Spread icing over cake. Top with blueberries. Allow icing to set. Serve.