I started out with a Genoese sponge by Alessandra Zecchini from her book Sweet As. Then used the Edmonds recipe for the chocolate icing.

I halved this recipe for the lamington sponge.

5 eggs, separated
140g sugar
grated lemon zest
120g flour (I used a bought gluten-free flour mix)
50g butter, melted

Preheat oven to 180C. Line base of 23 cm baking tin with baking paper, then grease and flour sides of tin.
Partly fill a small saucepan with hot water and set over medium heat. Set bowl over the simmering water and whisk egg yolks and sugar together until light and foamy. Remove from heat, add zest, flour, gradually, then melted butter. Beat egg whites until stiff peaks and fold into mixture.
Pour into tin and bake for 25 mins or until toothpick inserted into sponge comes out clean.
Cut into squares when cold.

Chocolate icing:
2 Tb butter
2 Tb cocoa (i like to use Valrhona from Sabato)
6 Tb boiling water
350g icing sugar
few drops vanilla extract

Melt butter, add cocoa dissolved in boiling water. Mix in sifted icing sugar, add vanilla essence, beat well.
Dip each square into the chocolate icing then roll in coconut. About 225g of coconut required for coating.