In a mixing bowl, combine flour,baking soda, salt and cornstarch, stir. Set aside.
In large mixing bowl, stir together the melted butter and both sugars until well blended. Add egg, egg yolks and vanilla.
Slowly add the four mixture mixing after each addition. The dough will be thick. When blended well, add the chocolate chips.
Cover bowl and chill for 2 hours or overnight. (after chilling-you may also roll dough into balls and freeze, baking only the amount you want.)
When ready to bake, let dough sit on counter for about 10 minutes.
Preheat oven to 325 f degrees. Line baking sheets with parchment paper.
Roll about 1oz (I use a scale) dough into balls and place on baking sheet about 2 inches apart.
Bake for 10-12 minutes. Cookies will have an under cooked look. (they will finish baking on the hot baking sheet) Leave on baking sheet for about 5 minutes before transferring to a cooling rack. Baking times may vary depending on your oven, the baking sheets, and size or cookie you choose to bake.