01 - Preheat the oven to 350°F. Grease an 8-inch square baking pan and line it with parchment paper.
02 - In a medium bowl, whisk together the all-purpose flour, baking powder, and salt. Set aside.
03 - In a large bowl, beat the softened butter and granulated sugar together using an electric mixer until light and fluffy, approximately 3 to 4 minutes.
04 - Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract until fully blended.
05 - Gradually add the flour mixture to the butter mixture, alternating with the whole milk, mixing gently after each addition until just combined. Avoid overmixing.
06 - Pour the batter into the prepared pan and smooth the top evenly. Bake for 20 to 25 minutes, or until a toothpick inserted into the center comes out clean.
07 - Allow the cake to cool completely in the pan. Turn it out onto a wire rack, then wrap tightly and freeze for 30 minutes to firm up for easier dipping.
08 - Combine the raspberries, water, granulated sugar, and lemon juice in a saucepan. Simmer over medium heat for 5 to 7 minutes, stirring occasionally. Strain through a fine mesh sieve to remove the seeds and let the syrup cool.
09 - Using a serrated knife, cut the cooled sponge cake into 12 even squares.
10 - Spread the desiccated coconut in a wide, shallow bowl. Dip each cake square briefly into the cooled raspberry syrup, allowing excess to drip off, then roll in the coconut to coat all sides evenly.
11 - For filled lamingtons, slice each coated square in half horizontally. Spread the bottom half with raspberry jam, pipe or spread whipped cream on top, then sandwich the halves together before the final coconut coating.
12 - Place the finished lamingtons on a wire rack and let them set for 15 minutes before serving.