01 - Preheat oven to 350°F. Line an 8-inch square baking pan with parchment paper, allowing overhang on two 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 unsalted butter and granulated sugar with an electric mixer on medium-high speed until pale, light, and fluffy, approximately 3 to 4 minutes.
04 - Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract until fully combined.
05 - Reduce mixer speed to low. Gradually add the dry ingredient mixture in three additions, alternating with the whole milk in two additions, beginning and ending with the dry ingredients. Mix only until just combined to avoid overworking the batter.
06 - Pour the batter into the prepared pan and spread evenly with a spatula. Bake for 22 to 25 minutes, or until a toothpick inserted into the center comes out clean. Allow the cake to cool completely in the pan on a wire rack.
07 - Once completely cooled, lift the cake from the pan using the parchment overhang. Trim any domed edges for even squares, then cut into 16 equal pieces. Place the squares on a tray and freeze for 30 minutes to firm up, which makes dipping much easier.
08 - In a wide bowl, whisk together the sifted powdered sugar and raspberry jam or puree. Add whole milk one tablespoon at a time until the glaze reaches a smooth, pourable consistency that coats the back of a spoon.
09 - Spread the desiccated coconut evenly in a shallow dish. Set up an assembly line with the chilled cake squares, raspberry icing, coconut dish, and a wire rack for finished pieces.
10 - Working one at a time, dip each chilled cake square into the raspberry icing, turning gently to coat all sides. Allow excess icing to drip back into the bowl, then immediately roll the coated square in the desiccated coconut, pressing lightly to adhere. Transfer to a wire rack to set for at least 15 minutes before serving.