Melt the butter in a very large, microwave-safe bowl. Once melted, refrigerate for 5 minutes. It's important the butter isn't hot when you add in the sugars or it will melt the sugar and make the cookies greasy.
Once butter is cooled to room temperature, stir in the light brown sugar and white sugar. Stir until smooth. Stir in the egg, vanilla extract, almond extract, coconut extract, and agave nectar. Mix until smooth.
Add in the cornstarch, salt, baking soda and baking powder. Again, stir until smooth. Add in the *correctly measured flour and mix until JUST combined. Don't overmix.
Gently stir in the white chocolate chips and macadamia nuts until combined.
Cover the bowl tightly and chill for 1 hour.
Preheat the oven to 350 degrees F. Line a baking sheet with parchment paper or use a nonstick liner.
Roll balls of dough into tall cylindrical balls (see picture above for shape and size). Place 6-8 cookie balls on the pan to give the cookies plenty of room to spread. Dough balls should be about 1.7 ounces.
Bake for 8-12 minutes, erring on the side of under-baking to keep them soft and chewy. (We like ours right at 9 minutes.) Remember, the cookies will bake a little more out of the oven, so take them out as soon as the edges start to lightly brown!
Remove from the oven and press a few additional chocolate chips or macadamia nuts in the top if desired (makes them look pretty). Allow to cool on the baking tray for 5 minutes before transferring them to a cooling rack.