Preheat the oven to 350 degrees Fahrenheit (175 degrees Celsius). Line a cookie sheet with parchment paper or a baking mat, and set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat together the butter, sugars, and vanilla extract (about 2 minutes until fluffy). Add the egg and mix, then add the egg yolk, mixing until just combined.
In a medium-sized mixing bowl, combine the flour, baking soda, baking powder, cornstarch, and salt. Whisk to combine. With the mixing speed on low, gradually add the dry ingredients and mix until just combined. Remove the bowl from the stand and fold in the coconut, toasted coconut, white chocolate chips, and chopped macadamia nuts. At this point, you can bake the dough right away or cover and chill it overnight for deeper flavor and better texture (which I recommend).
Scoop the cookie dough onto the prepared sheets using a standard-size cookie scoop. Place in the oven and bake for 10–12 minutes or until the edges are lightly golden. The centers should still look soft—don’t worry, they’ll finish setting as they cool. Overbaking will make them dry and hard. Let them cool on the sheet for 3 minutes before transferring to a wire rack to cool completely.
Notes
STORE Coconut White Chocolate Macadamia Nut Cookies in an airtight container at room temperature for up to 4–5 days to maintain their chewy texture and toasty flavor. If you want to extend their shelf life, FREEZE baked cookies in a single layer on a tray, then transfer them to a freezer-safe bag or container. They’ll keep well for about 2 months.Thaw at room temperature before serving. You can also freeze the unbaked dough—scoop it into balls and freeze it on a tray, then store it in a freezer bag. Bake straight from frozen, adding 1–2 minutes to the baking time.