Place butter and milk into the mixing bowl and heat 2 min/80°C/speed 2.
Add icing sugar and cocoa powder and mix 20-25 sec/speed 4. Scrape down the sides then pour into a deep bowl.
Cut the sponge into pieces. The size depends on how big you want your lamingtons. Place them on a wire rack with a sheet of baking paper under it.
Half fill another deep bowl with the coconut.
Using two forks (or your fingers if you don't mind getting them dirty - but just one hand), dip each piece of sponge in the chocolate icing to cover it then place it back on the rack to let the excess drip off.
Place the icing coated sponge one at a time in the coconut bowl and toss to coat. Once coated place in an airtight container. You may need to add more coconut to the bowl.