Line 2 large baking sheets with parchment paper or silicone baking mats. Set aside. Whisk together dry ingredients in a large bowl: flour, cornstarch, baking powder, baking soda, and salt. Set aside.
In a stand or electric handheld mixer, cream cold butter on medium to high speed until fluffy, about 1-2 minutes. Add in brown sugar and granulated sugar. Beat for an additional 2 minutes. Scrape down the sides of your bowl as needed. Add eggs one at a time, mixing after each addition until just combined. With the last egg, add in vanilla extract.
While mixer is running, add flour mixture 1/3 cup at a time until well combined, scraping down the sides as needed. Stir in both chocolate and caramel chips.
Using a cookie or ice cream scoop, scoop out dough and place on baking sheet. I used 40 grams (about 2 tablespoons) of dough for each cookie. This will make medium-sized cookies, like the ones pictured. Place pan in fridge and refrigerate for 30 minutes. Preheat oven to 365ºF or 185ºC.
Bake chilled cookies for 10-12 mins. Remove from the oven right when edges start getting golden. They may not look done, but they will continue to cook even after they've been removed from the oven. If desired, while the cookies are still warm, press a few extra chocolate and caramel chips into the tops and sprinkle with coarse sea salt. Let baked cookies cool on the baking sheet for 5 minutes. Then, transfer to a wire cooling rack to cool completely. We love these fresh out of the oven, but microwaved warm is delicious as well!