Cook the butter cake the day before you plan to eat the lammingtons so that the cake does not fall apart when it is iced and coconuted.
Line the base of a greased 27cm x 18cm lamington tin with baking paper.
Cream the butter and gradually add the sugar until the mixture is light and fluffy.
Gradually beat in the slightly beaten eggs, adding them one at a time, and beating until well-incorporated before adding the next.
Preheat your oven to 180C.
Sift the flour and salt together (you can do this a few times, which will help to make the cake lighter).
Gently fold the flour and salt into the creamed butter mixture, alternating the flour with the milk, be careful not to overwork the mixture.
Spread the mixture evenly in the prepared tins and bake for 30-35 minutes, or until cooked through (a skewer will come out clean).
Leave on a wire rack to cool completely.
Cut the butter cake into desired sized cubes or oblongs.
Dip into the chocolate icing and then immediately roll in the coconut. Leave on rack to set.