Start by preheating your oven to 180°C/160°C fan-forced and greasing a 4.5cm deep, 23cm x 33cm (base) roasting pan. Line base and sides with baking paper, spreading paper 3cm above edges of pan.
Using an electric mixer, beat eggs, sugar and vanilla together for 8 minutes or until mixture becomes thick and creamy.
Meanwhile, triple-sift cornflour, self-raising flour and plain flour together. Sift over egg mixture. Using a spatula or whisk, fold in flours until just combined. Fold in butter. Pour mixture into ready pan. Bake for 25 to 30 minutes or until sponge is golden and just firm to touch.
Turn onto a wire rack lined with baking paper. Cool fully. Trim edges of sponge.
Cut sponge into 24 squares.
Chocolate Icing
Place icing sugar, cocoa, milk and butter in a heatproof bowl over a pan of simmering water. Mixing over heat until combined and smooth. Place coconut in a bowl.
Using a fork, toss one piece of sponge in icing to coat. Drain off additional icing.
Mix in coconut to coat all over the lamington.
Once done transfer to a baking paper-lined tray.
Repeat process with your remaining sponge, icing and coconut.
Set aside for 1 hour to set and then enjoy!
Recipe by Art of Baking at http://www.artofbaking.net/lamingtons/