Using a hand mixer, beat together the melted butter, brown sugar and granulated sugar in a large bowl. Add in the vanilla extract, egg + egg yolk until the mixture is light and creamy, about 5 full minutes. This part is imparative in the chewiness of the cookie. Be sure to scrape the bottom of the bowl occasionally.
In a zip top bag or bowl, add the flour, baking soda, corn starch and salt and mix just until combined. Add dry mixture to the wet mixture, mix until just combined. Stir in the chocolate chips by hand with a spatula.
Scoop out cookie dough, about 1/4 cup per cookie, and form large, even dough balls until smooth. Place on a parchment lined baking sheet and freeze for about 30 minutes
Preheat oven to 325 degrees.
Bake for 10-12 minutes, rotating the pan halfway through and adding additional chocolate chips to the tops of the cookies. Cookies are done when the edges are slightly golden and center still looks under baked.
Let the cookies cool on the baking sheet for at least 5 minutes and then transfer to a wire racks to finish cooling. Add finishing salt if desired. Store in an airtight container.