Preheat oven to 400 degrees.
In a large bowl cream together butter, brown sugar and granulated sugar for 3 minutes on medium speed.
Add in eggs and vanilla and mix until well blended.
In a separate bowl whisk together flour, cornstarch, baking powder, baking soda and salt then slowly add to the wet ingredients.
Blend until the flour is halfway incorporated. You don't want to over mix the dough.
Add in the white chocolate chips and chopped macadamia nuts.
Finish mixing until the flour is just incorporated.
Using a large cookie scoop* or 1/4 cup measuring cup, scoop up dough and place onto a large plate.
Chill in the refrigerator for 1-2 hours.
Place 6 dough balls onto a baking sheet. Make sure to space them evenly apart.
Bake for 12-14 minutes or until lightly golden brown.
Add a few more white chocolate chips to the top of each cookie immediately after removing from the oven.
Let them cool for 5 minutes on the baking sheet then transfer to a cooling rack.
Repeat with the remaining dough.