Preheat the oven to 350°F (175°C) and prepare an 18x13-inch rimmed baking sheet by lightly spraying it with flour spray and lining it with parchment paper.

In a large mixing bowl, combine the softened unsalted butter and granulated sugar, beating on medium speed for about 3-4 minutes until light and fluffy.

Add the eggs one at a time, beating well after each addition, then stir in the vanilla and coconut extracts until combined.

In a separate bowl, whisk together the all-purpose flour, desiccated coconut, baking powder, and salt.

Gradually add the dry mixture to the butter mixture, alternating with the coconut milk, mixing gently until just combined.

Pour the batter into the prepared baking sheet, smoothing the top, and bake for 15-18 minutes until a wooden pick comes out clean.

Allow the cakes to cool completely in the pan for about 30 minutes, then use a 2¼-inch round cutter to cut out 36 rounds.

Pipe a layer of White Chocolate Buttercream on top of 12 cake rounds, stack another round, and pipe more buttercream before topping with the final cake round.

Decorate the tops by piping rosettes of White Chocolate Buttercream and garnish with mint leaves if desired.