Heat the oven to 180 C / 350 F. Grease a 23x33 cm / 9x13-inch baking pan and line it with parchment.

Cream the butter and sugar in a large bowl with a hand mixer for 3 to 4 minutes, until pale and fluffy.

Add the eggs one at a time, beating well after each, then mix in the vanilla extract.

Whisk the flour, baking powder, and salt together in a separate bowl. Add to the butter mixture in three additions, alternating with the milk, mixing just until smooth.

Spread the batter into the prepared pan and smooth the top with a spatula. Bake for 25 to 30 minutes, until a toothpick inserted in the center comes out clean and the top springs back when pressed.

Cool the cake in the pan for 10 minutes, then lift onto a wire rack to cool completely, about 45 to 60 minutes, before icing.

Sift the powdered sugar into a medium bowl. Whisk in the water or lemon juice one tablespoon at a time until the icing is thick but pourable.

Add 1 to 2 drops of pink food coloring and stir until the icing turns an even pale pink.

Pour the icing over the cooled cake and spread it to the edges with an offset spatula.

Scatter the desiccated coconut evenly over the wet icing before it starts to set, within about 5 minutes.

Let the icing set at room temperature for 20 to 30 minutes, then cut into 16 squares.