Move oven rack to middle position and preheat to 350 ° F.
Line a 9x13-inch baking pan with foil. Lightly spray the foil with nonstick cooking spray; set aside.
BROWN THE BUTTER:
In a 10-inch skillet over medium-high heat, add 10 tablespoons of butter and heat until melted, and the butter turns dark golden brown while swirling the pan often. Take the pan off the heat and swirl in the remaining 4 tablespoons of butter.
MAKE THE BATTER:
In the bowl of a stand mixer fitted with the whisk attachment, add the butter, sugars, salt, and vanilla and mix until combined.
Add the egg and yolk and mix for 30 seconds, and then let the mixture rest for 3 minutes.
Repeat the mixing and resting process 2 more times; the mixture will be thick, smooth, and shiny.
Sift in the flour and baking soda and fold in using a rubber scraper until just combined. Fold in the white chocolate chips, macadamia nuts, and coconut until evenly distributed.
Spread the batter in the prepared pan.
BAKE AND COOL:
Bake for 30-35 minutes, or until the middle of the bars are puffy and the edges are golden brown. They will be on the gooey side, and when a toothpick is inserted, it will NOT come out clean. This is ok, and how it should be!
Transfer the pan to a wire rack and cool completely for about 60-90 minutes.
MELT CHOCOLATE AND TOP:
Place white chocolate chips and butter in a microwave-safe bowl.
Heat in the microwave for 1 minute on 50% power. Stir and heat again for 30 seconds at 50% power. Stir. Repeat the process until the white chocolate is melted completely.
Spread the chocolate evenly over the cooled bars. Top with toasted macadamia nuts and coconut.
CHILL, SLICE, AND SERVE:
Transfer the bars to chill the refrigerator for 1 hour.
Remove the bars from the pan using the foil overhang.
Slice into 24 bars and serve!
This recipe calls for toasted, shredded coconut. To toast the coconut, heat a large skillet over medium heat. Add the coconut and frequently stirring until the coconut is mostly all golden brown, about 3-6 minutes.
You can use this same process to toast the macadamia nuts.
When I make these for bake sales, I slice them into 12 bars to be a little larger.
This recipe is best with high-quality white chocolate like Ghirardelli white baking chips.