Preheat oven to 375°F (190°C).

Grease and flour an 8x12 inch rectangular pan.

Sift together the flour, baking powder, and salt in a bowl.

In a large bowl, cream together the butter, sugar, and vanilla extract until light and fluffy.

Add the eggs one at a time, beating well after each addition.

Gradually add the flour mixture alternately with the milk, beating well after each addition.

Pour the batter into the prepared pan.

Bake in the preheated oven for 30 to 40 minutes, or until a toothpick inserted into the center comes out clean.

Let the cake stand for 5 minutes before turning it out onto a wire rack to cool completely.

Store the cake overnight to allow it to firm up before icing.

To make the icing, combine icing sugar and cocoa powder in a large bowl.

In a saucepan, heat milk and melted butter until the butter is melted and the mixture is warm.

Add the warm milk mixture to the sugar mixture and mix well to create a fluid, but not too runny, icing.

Cut the cooled cake into 24 squares.

Place flaked coconut in a shallow container.

Using a fork, dip each cake square into the chocolate icing, ensuring it is fully coated.

Immediately roll the iced cake square in the flaked coconut, pressing gently to adhere.

Place the coconut-covered lamington onto a wire rack to dry.

Repeat the dipping and coating process for each cake square.

Allow the lamingtons to dry completely, placing something underneath the rack to catch any drips.