Preheat your oven to 350°F (175°C). Lightly grease a 12-inch round pizza pan, cake pan, or baking dish with butter or neutral oil. Line the bottom with parchment paper to facilitate easy removal once baked.

In a medium mixing bowl, whisk together the flour, cornstarch, baking soda, and kosher salt until evenly incorporated. Set aside.

In a separate large mixing bowl, use an electric mixer to cream the softened butter with the light brown sugar and granulated sugar. Beat for 2 to 3 minutes until the mixture becomes light in color and fluffy in texture.

Add the egg and vanilla extract to the creamed mixture. Beat until the ingredients are thoroughly combined and smooth.

Gradually add the dry ingredients to the wet mixture. Mix on low speed until just combined, taking care not to overmix. Gently fold in the milk chocolate chips using a spatula or wooden spoon.

Transfer the cookie dough to the prepared pan. Use clean hands or a spatula to press the dough evenly across the surface of the pan. For an enhanced presentation, press a few additional chocolate chips into the top of the dough before baking.

Bake in the preheated oven for 10 to 12 minutes, or until the edges are lightly golden and the center appears set but soft. Allow the cookie to cool completely in the pan before slicing into wedges and serving.