Sift the flour, cornstarch, baking soda, and salt together in a large bowl. Set aside.
In a separate bowl or mixer, whisk the melted butter, brown sugar, granulated sugar, eggs and vanilla extract together until combined.
Pour into the dry ingredients and use a rubber spatula mix together till just combined.
Fold in the sea salt caramel chips and chopped macadamia nuts.
Measure out a large piece of plastic wrap on the counter and spread out the dough into a rough log shape. Wrap in plastic wrap to form a log. Use your hands to roll it into a uniform log. The diameter of the log will be the size of your cookie, so keep that in mind when rolling. I generally like to keep my cookies bite sized so the diameter of my log is about 2 inches (5 cm).
Chill in the refrigerator for at least 20-30 minutes.
Preheat oven to 350F (177C). Line a baking sheet with parchment or a silicone baking mat.
Remove from fridge. Unwrap the plastic wrap and use a sharp knife to slice your cookies. Approximately 1/2 inch (1 cm) thick. At this point you can freeze the cookies you don't plan on baking right away. (Don't forget to label the container with the baking instructions for later!). You can bake these cookies straight from frozen (no need to defrost!) - see below for more tips on freezing the dough.
Place the cut cookies on the baking sheet about 2 inches apart.
Bake 12-13 minutes or until lightly brown on the sides. The centre will still look a bit soft. It will firm up as it cools.
Remove from the oven and allow to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool.
Baked cookies will keep at room temperature for about 4-5 days. Frozen cookie dough can keep for months in the freezer.