Cake: Preheat the oven to 180 degress C. Cover a lamington tray with non-stick spray.
Cream the butter and sugar until light and fluffy then add the eggs one at a time alternately with the milk beating well after each edition. Add the vanilla and give the final beat to combine well but don't over beat.
Spread the batter evenly into the lamington tray then bake in the preheated oven for 25 to 35 minutes, or until cooked.
Turn out onto a cooling rack. When cold cut into 30 squares.
Chocolate Icing: Melt the butter in a 1/4 cup of boiling water. In a bowl sift the icing sugar with the cocoa then slowly add the butter liquid and vanilla. Stir well, the icing will be very thin. More hot water may need to be added.
Dip each square cake piece into the icing then in the coconut. Let sit for an hour before serving.