01 - Preheat the oven to 350°F (175°C). Line an 8-inch square baking pan with parchment paper, allowing slight overhang on the sides for easy removal.
02 - In a medium bowl, whisk together the all-purpose flour, baking powder, and salt until evenly distributed. Set aside.
03 - In a large mixing bowl, beat the softened butter and granulated sugar with an electric mixer on medium-high speed until pale, light, and fluffy, approximately 3-4 minutes.
04 - Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract until fully incorporated.
05 - Gradually add the dry ingredient mixture to the butter mixture in three additions, alternating with the whole milk in two additions. Mix on low speed just until combined — avoid overmixing to keep the sponge light.
06 - Spread the batter evenly into the prepared baking pan, smoothing the top with a spatula. Bake for 22-25 minutes, or until a toothpick inserted into the center comes out clean. Allow the cake to cool completely in the pan.
07 - Once completely cool, lift the cake from the pan using the parchment overhang. Trim any domed edges if needed, then cut into 16 equal squares. Place the squares on a tray and freeze for 30 minutes — this firms them up and makes the dipping process much easier.
08 - In a shallow bowl, whisk together the sifted powdered sugar, raspberry jam or puree, and 2 tablespoons of whole milk. Add additional milk one teaspoon at a time until the icing reaches a smooth, pourable consistency that coats the back of a spoon.
09 - Spread the desiccated coconut in a shallow dish. Using a fork or your fingers, dip each chilled cake square into the raspberry icing, allowing the excess to drip off briefly. Immediately roll the iced square in the coconut, pressing gently to coat all sides evenly. Transfer to a wire rack to set.
10 - Allow the lamingtons to rest on the wire rack at room temperature for at least 30 minutes until the icing firms up. Serve at room temperature or slightly chilled.