In a small pan, melt 9 tbsp unsalted butter over medium heat, stirring frequently. You want the butter to turn golden and have small brown specks on the bottom (it’ll smell nutty). Transfer the brown butter to a heatproof bowl and allow to cool slightly (about 30 minutes room temperature).
To a large mixing bow, combined the slightly cooled brown butter, light brown sugar, and white sugar, whisking together until combined. Add the egg, vanilla bean paste, and heavy cream. Whisk until combined and the color becomes lighter in appearance (about 2-3 minutes).
Add in the flour, baking powder, baking soda, and salt. Use a rubber spatula and fold the mixture together, leaving behind a few streaks of flour. Add the white chocolate chips and chopped macadamia nuts and fold the mixture together until it’s just combined.
Scoop the cookie dough into 10 balls. Roll each ball and place on a cookie sheet. Cover and place in the freezer to chill for 30 minutes. During this time, preheat the oven to 350 degrees.
Place the cookie dough balls out on a parchment lined cookie sheet (you can do all 8 on one sheet or two separate cookie sheets). Bake for 12-14 minutes, cookies will be just set around the edges.
As soon as the cookies come out of the oven, sprinkle the cookies with flaky sea salt if desired.
Allow cookies to cool on a cookie sheet for 10 minutes, then place on a cooling rack to finish cooling off.