Cream The Butter & Sugars. In the bowl of a stand mixer or a large mixing bowl, cream softened butter, sugar, and brown sugar on medium speed for 2-3 minutes, or until light and fluffy.
Finish Wet Ingredients. Scrape down the edges of the mixing bowl and add eggs one at a time, beating until fully incorporated before adding the next egg. Add in the vanilla and mix until blended.
Add The Dry Ingredients. Scrape down the sides of the bowl again and add gluten-free flour blend, cornstarch, baking soda, baking powder, and salt. Mix until *almost* all the way incorporated and there's just a little powdery flour left in the batter.
Fold In The Chocolate & Nuts. Add the white chocolate chips and chopped macadamia nuts and stir them in just until they're evenly distributed.
Chill At Least 2 Hours. Cover and chill the dough in the fridge for 2 hours (up to 24 hours). Do NOT skip the chill time, or the cookies will spread too much!
Preheat The Oven & Prep Your Pans. When you're ready to bake the cookies, preheat the oven to 350 degrees F. Line two baking sheets with parchment paper so you can alternate pans between batches.
Scoop & Bake Cookies. Use a large (3 tablespoon) cookie scoop to scoop 6 balls of cookie dough onto a prepared baking sheet. (Bake just 6 cookie dough balls at a time so they don't crowd the pan and run into each other.) Bake at 350 degrees for 9-11 minutes, or until the edges are just golden brown and the centers look slightly underdone. (Return the rest of the dough into the refrigerator while the cookies are baking.)
Cool & Repeat. Remove the baked cookies from the oven and cool on the baking sheet for 2 minutes before transferring to a wire rack to finish cooling. Repeat baking process with remaining cookie dough, alternating between cookie sheets so you don't put cold dough on a hot sheet pan (which can impact the spread and the evenness of the bake). Enjoy cooled cookies right away, and store leftover cookies in an airtight container at room temperature 2-3 days (or freeze up to 2 months).
*For Extra Pretty Cookies* use a large round cookie cutter to gently shape the hot cookies into perfect circles right after you pull them out of the oven. Garnish with a few extra white chocolate chips + macadamia nuts.