Preheat the oven to 350°F (175°C). Butter the bottom and sides of a 9 × 13-inch baking pan. Line the pan with a long sheet of parchment paper, allowing the parchment to extend up the short sides and slightly overhang the edges. Butter the parchment and set the pan aside.

In a medium bowl, whisk together the flour, baking powder, and salt until evenly combined. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment, cream the softened butter and brown sugar on medium speed until the mixture is light and fluffy.

Add the eggs and vanilla extract, mixing until the batter is smooth and lighter in color, approximately 1 to 2 minutes.

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

Stir in ¼ cup of the chopped macadamia nuts, ½ cup of the chopped white chocolate, and the toasted coconut. Spread the batter evenly into the prepared baking pan.

Sprinkle the remaining ¾ cup shredded coconut and remaining macadamia nuts evenly over the surface of the batter.

Bake for 34 to 36 minutes, or until a toothpick inserted into the center comes out clean. Remove from the oven and allow the blondies to cool completely in the pan on a wire rack.

Place the remaining ½ cup white chocolate in a heatproof metal bowl set over a saucepan of gently simmering water. Stir occasionally until melted and smooth. Remove from heat.

Transfer the melted white chocolate to a resealable plastic bag. Snip a small corner and drizzle the chocolate evenly over the cooled blondies.

Once the chocolate has set, lift the blondies from the pan using the parchment overhang and cut into 24 bars.