Preheat oven to 400°F
Whisk together all-purpose flour, corn starch, baking soda, and salt in a separate bowl.
Add cold, cubed butter to stand mixer fitted with the paddle attachment, and mix on high for 1 min. Scrape sides, mix again for another 30 seconds.
Add brown sugar and granulated sugar to butter and mix on medium until combined and fluffy.
Add vanilla extract, egg, and egg yolk until just combined. (don't overmix!)
Start adding flour mixture in increments on low until just combined, don't turn mixer on too high or you could end up with flour all over your kitchen!
Add the chocolate chips, I like to use both semi-sweet and milk chocolate chips. Pulse mixer a few times to disperse the chocolate chips.
Roll each cookie and place on a parchment lined baking sheet. These cookies weighed about 160 grams each (6 oz) and I was able to form 6 giant cookies!
Pro Tip: If you'd like to add chocolate chips to the tops before baking, gently press them upside down into the cookie. This keeps the tips of the chocolate chips from burning!
Bake on middle rack for 10-12 minutes, depending on cookie size. The cookies should start turning light brown on the tops!
Let sit for 10-15 minutes after baking before moving to a cooling rack, this gives the cookies time to set!