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

In a medium bowl, combine melted butter, brown sugar, and granulated sugar. Whisk until smooth and creamy.

Add the whole egg, egg yolk, and vanilla extract to the wet mixture, whisking until incorporated.

Gently fold the dry mixture into the wet mixture until just combined, avoiding overmixing.

Fold in the chocolate chips gently.

Cover bowl with plastic wrap and refrigerate the dough for at least 30 minutes.

Preheat oven to 325°F (163°C) and line baking sheets with parchment paper.

Scoop about 1.5 tablespoons of dough onto prepared baking sheets, spacing them 2 inches apart.

Bake for approximately 13 minutes or until edges are golden brown but centers look soft.

If desired, press extra chocolate chips into the tops after baking. Cool on the baking sheet for 10 minutes before transferring to a wire rack.