In a large bowl, whisk together flour, baking powder, and salt.

In a large mixing bowl using an electric hand mixer or a stand mixer fitted with a paddle attachment, beat the butter and sugar together until light and fluffy, 2 to 3 minutes.

Add the eggs, one at a time, beating until combined between each. Stopping to scrape down the sides as needed. Beat in the vanilla.

With the mixer on low speed, add a third of the flour mixture, followed by half of the milk. Repeat, alternating between another third of the flour mixture and the remaining milk until both are fully combined. Stop to scrape down the bowl occasionally. Pour batter into the prepared pan.

Bake for 18 to 20 minutes, or until a wooden pick inserted into the center comes out clean. Let the cake cool in the pan for 20 minutes. Invert onto the cooling rack, remove the parchment paper and let cool completely.

Once cooled completely, cut the cake into 24 (2-inch) squares. (Trim off the edges if they are a bit crisp.)

In a medium bowl, whisk together sugar, cocoa powder, butter, and boiling water until smooth.

Line a baking sheet with parchment and place a wire rack on top. Pour desiccated coconut into a small shallow bowl.

Using a fork to move the pieces of cake, coat the cake squares in the icing. Allow the excess icing to drip off before moving to the coconut and rolling to coat. (If the chocolate icing hardens while coating, stir in a splash of hot water or more until the desired consistency is reached. )

Place the coated cake square onto the prepared rack to dry. Repeat with remaining cake squares. Let dry completely before serving, about 20 minutes. Store in an airtight container at room temperature for 3 to 4 days.