Cut the sponge cake into approximately 20 small squares.
Mix the jelly crystals and icing sugar together and add boiling water and melted butter. Stir until smooth, adding a little extra water if required, to make a thin, pourable icing. Dip each sponge square into the icing. Sprinkle with the coconut and dry on a piece of baking paper spread on a wire rack.
Serve the lamingtons with fresh raspberries and softly whipped cream or ice cream, if desired.
Tip: use two forks for the rather fiddly job of slipping the sponge into the icing. Sometimes it’s easier to pour the icing over the sponge held on a fork; however, practice does make perfect.