Preheat the oven to 350°F (175°C). Butter the bottom and sides of a 9-by-13-inch baking pan. Line the bottom with parchment paper, allowing it to overhang slightly on the two short sides. Butter the parchment as well.

In a medium-sized mixing bowl, whisk together the flour, baking powder, and salt. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment, cream the softened butter with the brown sugar until the mixture is light and fluffy. Add the eggs and vanilla extract, blending until pale in color, approximately 1 to 2 minutes.

Gradually add the flour mixture to the creamed butter mixture, mixing until just combined. Do not overmix.

Stir in ¼ cup of the chopped macadamia nuts, ½ cup of the chopped white chocolate, and the toasted ½ cup of shredded coconut until evenly distributed.

Spread the batter evenly into the prepared baking pan. Sprinkle the surface with the remaining ¾ cup of sweetened shredded coconut and the remaining macadamia nuts.

Place the pan in the oven and bake for 34 to 36 minutes, or until a toothpick inserted into the center comes out clean. The edges should be golden brown.

Remove the pan from the oven and allow the blondies to cool completely on a wire rack before proceeding.

Melt the remaining ½ cup of chopped white chocolate in a metal bowl placed over a saucepan of gently simmering water. Stir occasionally until the chocolate is smooth. Remove from heat.

Transfer the melted white chocolate into a resealable plastic bag. Snip a small corner off the bag and drizzle the chocolate over the cooled blondies. Once the drizzle has set, lift the blondies out of the pan using the parchment overhang and cut into 24 squares.