Chewy Chocolate Chip Cookies

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

In a medium bowl, whisk the melted butter, brown sugar, and granulated sugar together until no brown sugar lumps remain. Whisk in the egg, then the egg yolk. Finally, whisk in the vanilla extract. Pour the wet ingredients into the dry ingredients and mix together with a large spoon or rubber spatula. The dough will be very soft, yet thick. Fold in the chocolate chunks. They may not stick to the dough because of the melted butter, but do your best to combine them. Cover the dough and chill in the refrigerator for 2-3 hours or up to 3-4 days. Chilling is mandatory. I highly recommend chilling the cookie dough overnight for less spreading. (Some readers have asked if it’s possible to roll into balls and then chill, but I don’t recommend it. The cookie dough is quite sticky and loose to section into balls before chilling.)