Preheat oven to 350°F; line baking sheets with parchment. Whisk flour, baking soda, cornstarch, and salt in a medium bowl.
Mix melted butter and both sugars in a large bowl; beat in eggs, yolk, and vanilla until smooth and thick.
Stir in flour mixture just until no streaks remain; fold in chocolate chips evenly.
Use a large scoop to place tall dough mounds 3 inches apart on prepared sheets. Bake 12-14 minutes, until edges are golden and centers look slightly underdone.
Cool completely on sheet to set and retain shape.