Directions

1. Whisk the flour, cornstarch, baking soda, and salt together in a large bowl. Set aside.
   
2. Whisk the melted butter, brown sugar, granulated sugar, egg, egg yolk, and vanilla extract together until combined. Pour into dry ingredients and mix everything together with a rubber spatula until completely combined. Fold in the white chocolate chips and macadamia nuts.
   
3. Cover and chill the dough in the refrigerator for at least 2 hours and up to 4 days. If chilling for longer than 2 hours, allow to sit at room temperature for at least 20-30 minutes before rolling and baking because the dough will be quite hard.
   
4. Preheat oven to 350°F. Line baking sheets with parchment paper or silicone baking mats. Set aside. Roll cookie dough into balls, about 1-1 1/2 tablespoons of dough per cookie, and arrange 3 inches apart on the baking sheets.
   
5. Bake for 12-13 minutes or until lightly browned on the sides. The centers will look soft. Remove from the oven and allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely. Cookies stay fresh covered at room temperature for up to 1 week.