Preheat oven to 325°F (163°C) and line baking sheets with parchment paper.
In a bowl, whisk together flour, cornstarch, baking soda, and salt.
In a separate large bowl, beat butter, brown sugar, and granulated sugar until creamy.
Add egg, egg yolk, and vanilla extract, mixing until smooth.
Gradually mix in the dry ingredients until combined.
Fold in chocolate chips until evenly distributed.
Divide dough into 6 large portions and shape into thick mounds.
Place cookies on baking sheets, leaving space between each.
Bake the Giant Chocolate Chip Cookies for 20–25 minutes until edges are lightly golden.
Let cool on the baking sheet for 15 minutes, then transfer to a wire rack.