Chocolate buttercream 125g butter, at room temperature 185g (1½ cups) icing sugar, sifted 2 tablespoons cocoa powder, sifted
Preheat oven to 180°C (160°C fan-forced). Grease a square 20cm cake tin with melted butter and line the base with non-stick baking paper.
Combine the butter, sugar and milk in a medium saucepan. Stir over medium heat until butter melts, sugar dissolves and mixture is combined (see Baker's Tips). Remove from heat and use a fork to whisk in the eggs and vanilla.
Sift together the flour, cocoa powder and baking powder into a large bowl. Stir in the coconut. Add the butter mixture and use a balloon whisk to stir until just combined.
Spoon the mixture into the prepared tin and use the back of a metal spoon to smooth the surface. Bake in preheated oven for 30-35 minutes or until a skewer inserted into the centre of the cake comes out clean. Stand in the tin for 5 minutes before turning onto a wire rack to cool (this will take about 1½ hours).
To make the Chocolate buttercream, use an electric mixer to beat the butter, icing sugar and cocoa powder in a medium bowl until pale and creamy and it is a smooth spreadable consistency. Spread the cooled cake with the buttercream and cut into portions to serve.
Don’t overheat the butter mixture – as soon as the butter melts and the sugar has dissolved, remove it from the heat.
This cake will keep in an airtight container at room temperature in a cool spot for up to 3 days.