Whisk together the flour, baking soda, cornstarch and salt in a large bowl. Set aside.

In a medium size bowl, whisk the melted butter, brown sugar, and white sugar together until no brown sugar lumps remain. Whisk in the egg, then add the extra egg yolk. Finally, whisk in the vanilla. Pour the wet ingredients into the dry ingredients and mix together with a large spoon or rubber spatula. Fold in the chocolate chips. Cover the dough and chill in the refrigerator for 1 hour. do not skip the chilling step.

Take the dough out of the refrigerator and allow to set for about 5 minutes

Preheat the oven to 325°F. Line two large baking sheets with parchment paper or silicone baking mats. Set aside.

Roll the chilled dough into balls, about 3 Tablespoons of dough each. Then place on prepared sheet Continue this process until all the dough has been rolled. Bake the cookies for 12-13 minutes. These cookies will continue to bake on the cookie sheet. Let them set for 5 minutes them transfer them to a wire rack.

**you can use regular chocolate chips/chunks if you desire