Preheat oven to 350°F and line baking sheets with parchment paper, then whisk together flour, baking soda, cornstarch, and salt in a medium bowl.
In a large bowl, mix melted butter with both sugars until combined, then add eggs, egg yolk, and vanilla, beating until smooth and thick.
Stir in the flour mixture until just combined and no streaks remain, then fold in chocolate chips until evenly distributed.
Use a large cookie scoop to portion dough into tall mounds on prepared baking sheets, spacing them 3 inches apart, and bake for 12-14 minutes until edges are golden but centers look slightly underdone.
Let cookies cool completely on the baking sheet to allow them to set and maintain their thick shape.