*the dough needs to chill for one hour before baking
Find a round cookie cutter or small bowl about 4 inches in diameter to use for scooting the cookies.
Cut the cold butter into cubes.
Cream the cold butter, brown sugar, and granulated sugar on medium speed until a paste forms, about 2 minutes.
Add the cold egg, extra yolk, and vanilla. Mix until combined, about 20 seconds. Scrape down the bowl.
In a separate bowl, whisk together the flour, baking soda, cornstarch, and salt until evenly blended.
Add the dry ingredients to the butter mixture. Mix on low speed until almost combined. Scrape down the bowl.
Fold in the chocolate until just combined, making sure the chips are evenly distributed. Do not over mix.
Portion the dough into 65 gram balls, roll them, and place them on a plate or baking sheet that fits in the refrigerator. Chill the dough for 1 hour. You can also make 20 smaller cookies (bake for 8-10 minutes)
Preheat the oven to 350°F about 30 minutes before baking.
Place 4 dough balls at a time on a parchment-lined baking sheet. Keep the remaining dough balls in the refrigerator.
Bake for 11 to 13 minutes on the center rack of the oven, until the cookies are golden at the edges and soft in the center. Do not over bake.
Right when the cookies come out of the oven, use your cookie cutter or bowl to gently scoot around the edges, making them thicker, rounder, and perfectly crinkly. Work carefully so you only move the edges, not the whole cookie. Let the cookies cool completely on the baking sheet until set.