Begin by Browning your Butter:

Cup of Yum
1. Place butter in a medium-sized saucepan over medium-low heat.
2. Once butter has melted, increase heat to just above medium heat. Stir the butter and scrape the sides and bottom of the pan frequently with a wooden spoon or heatproof spatula - the butter will begin to bubble and pop. Once the bubbling/popping slows, the butter will begin to turn brown (see image). Once it begins to brown, remove from heat and pour into a large heat-proof bowl.
3. Allow butter to cool to room temperature before proceeding with the recipe.

Cookie Dough

1. Add sugars into cooled browned butter and stir well.
2. Add eggs and vanilla extract and stir until well-combined.
3. In a separate, medium-sized bowl, whisk together flour, cornstarch, baking powder, baking soda and salt.
4. Gradually add flour mixture to butter mixture, stirring until ingredients are nearly completely combined.
5. Add white chocolate chips and macadamia nut pieces and stir until ingredients are well-incorporated.
6. Cover bowl with plastic wrap and chill cookie dough in the refrigerator for at least 30 minutes before proceeding.
7. 15 minutes before you are ready to bake cookies, preheat oven to 350F (175C) and line cookie sheets with parchment paper. Once oven is preheated and cookie dough has chilled, drop dough by heaping, rounded 1 ½-Tbsp-sized scoops (50g) onto prepared cookie sheets, placing at least 2" (5cm) apart.
8. Bake on 350F (175C) for 9-11 minutes or until edges are just beginning to turn golden brown (cookies should still be quite soft when you remove them from the oven, and may even appear slightly underbaked in center).
9. Sprinkle lightly with sea salt immediately after removing from the oven.
10. Allow cookies to cool completely on baking sheet.