In a large bowl, whisk the flour, baking soda, cornstarch, and salt together. Set aside.

In a medium bowl, whisk the melted butter, brown sugar, and granulated sugar together until no lumps remain. Whisk in the egg and egg yolk until combined, then whisk in the vanilla extract.

Pour the wet mixture into the dry ingredients and mix together with a large spoon or spatula until the dough is very soft, thick, and shiny. Fold in the chocolate chips.

Cover the dough tightly and refrigerate for at least 2 hours or up to 3 days.

Preheat the oven to 325°F (163°C). Line large baking sheets with parchment paper.

Using a cookie scoop, scoop the chilled cookie dough, and roll into a ball. Shape the cookie dough to be taller rather than wide.

Arrange the cookies 3 inches apart on the prepared baking sheets.

Bake the cookies for 13–14 minutes or until the edges are very lightly browned. Cool on the baking sheet for 10 minutes before transferring to a cooling rack to cool completely.