Add flour, baking soda, cornstarch, and salt in a small bowl. Whisk to combine.
Add butter to large saucepan over medium heat. Butter will begin to foam and then brown quickly. Stir constantly during entire process. Once butter begins to brown, remove from heat and pour into a glass measuring cup. Set aside to cool for 10 minutes.
Add cooled brown butter to a medium bowl. Add light brown sugar and granulated sugar and mix until combined.
Add vanilla extract, egg, and egg yolk. Mix until combined.
Add flour mixture into butter mixture and stir until just combined.
Fold in the white chocolate chips until evenly distributed.
Fold in the macadamia nuts until evenly distributed.
Cover the bowl and place in refrigerator for 30 minutes.
Preheat oven to 350° F. Line a baking sheet with parchment paper. Scoop out 12 cookies using a #20 (3 tablespoon) cookie scoop.
Add extra white chocolate chips and macadamia nuts on top for a bakery-worthy cookie.
Bake for 12-13 minutes.
Set aside to cool and then enjoy!