Preheat the oven to 350ºF. Line a 9x9" baking dish with parchment paper.
In a mixing bowl, combine the flour, baking soda, baking powder and salt. Stir until mixed well.
In a large mixing bowl, combine softened butter, brown sugar and granulated sugar. Mix with an electric mixer until well blended.
Add the egg and vanilla extract and mix again until combined.
Slowly add flour mixture to butter mixture, mixing as you go until it's all just combined. It is important not to overmix.
Add white chocolate chips and macadamia nuts and stir until combined.
Spread cookie batter into the baking pan. Spread evenly and smooth with a spatula. Add 10-20 more chocolate chips to the top, if desired.
Cook for 20-22 minutes or until golden and cooked to your desired crispiness. Remember it will continue cooking a little after you remove it from the oven.
Once cool, remove from the baking dish and cut into 16 pieces.