Preheat your oven to 350°F (175°C) and grease an 8-inch square cake pan with butter.

In a mixing bowl, cream together the softened butter and sugar until light and fluffy, about 3-4 minutes.

Add in the eggs, one at a time, continuing to mix until fully incorporated.

Gradually fold in the self-raising flour and milk until you achieve a smooth batter.

Pour the lamington batter into the prepared cake pan, smoothing the top with a spatula.

Bake in your preheated oven for approximately 25-30 minutes until golden brown and a toothpick comes out clean.

Allow the cake to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.

While the cake cools, melt the butter for spreading and combine the rainbow sprinkles and desiccated coconut in a bowl.

Cut the cooled cake into squares or rectangles about 2 inches in size.

Dip each piece into the melted butter, then roll in the sprinkles and coconut mixture until evenly covered.

Place the coated lamingtons on a serving platter and add more sprinkles for decoration if desired.