Preheat your oven to 350 degrees F. Line two baking sheets with parchment paper.

Grate the zucchini on the large holes of a box grater. Transfer it to a clean kitchen towel and squeeze out as much liquid as possible. Keep squeezing until the zucchini feels nearly dry. This is the most important step for getting cookies that bake up properly rather than spreading into flat puddles.

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

In a large bowl, beat the softened butter with both sugars using a hand mixer or stand mixer on medium speed for about 2 minutes, until light and fluffy. Add the egg and vanilla and beat until smooth, scraping down the sides of the bowl as needed.

Add the squeezed zucchini to the butter mixture and mix on low just until incorporated. The mixture may look slightly broken or curdled at this point, which is fine.

Add the flour mixture and mix on low until just combined. Fold in the white chocolate chips and chopped macadamia nuts with a rubber spatula, making sure they are evenly distributed throughout the dough.

Scoop rounded tablespoons of dough onto the prepared baking sheets, spacing them about 2 inches apart. Press each mound down very slightly with your fingertips so they are not domed too high.

Bake one sheet at a time on the center rack for 11 to 12 minutes, until the edges are set and very lightly golden but the centers still look soft. They will continue to firm up on the pan.

Let the cookies rest on the pan for 2 full minutes before transferring them to a wire rack. They are delicate when hot and need that resting time to hold together as you move them. Cool completely before storing.