Preheat your oven to 350°F (175°C) to ensure even baking.
In a medium bowl, whisk together the all-purpose flour, cornstarch, baking soda, and salt.
In a large mixing bowl, combine the melted butter, light brown sugar, and granulated sugar. Whisk until smooth and creamy.
Add the egg, egg yolk, and vanilla extract to the sugar mixture and whisk until well combined.
Gradually add the dry ingredients to the wet ingredients, mixing just until combined.
Gently fold in the miniature semisweet chocolate chips until evenly distributed.
Using a cookie scoop, drop rounded tablespoons of dough onto lined baking sheets, leaving space between each cookie.
Bake for 10-12 minutes, until the edges are lightly golden and the centers look slightly underbaked.
Remove from the oven and let cool on the baking sheets for about 5 minutes before transferring to a cooling rack.