Preheat oven to 375 degrees.

1. Whisk together the flour, salt, cornstarch and baking soda in a medium bowl and set aside.
2. Add the butter to the bowl of a stand mixer, or use a hand mixer.  Mix on medium-high speed until the butter is very light and creamy, about one minute.
3. Add the sugars and mix on high speed until all of the sugar is dissolved and there are no lumps remaining in the brown sugar, about one minute.
4. Add the egg, egg yolk, and vanilla and mix on medium speed just long enough to combine about 30 seconds.
5. Add one cup of the flour, and mix just until almost incorporated, no more.  Add the second cup of flour and mix until the flour is about halfway incorporated.  Stop mixer and add the chocolate chips and mix on medium speed until the flour is incorporated and stop the mixer.  Do not over mix.
6. Using a large cookie/ice cream scoop, (see note below**) place scoops of dough on a cookie sheet that has been lined with parchment paper.  The parchment paper will help the cookies from spreading too thin.  They will already be thin, trust me.
7. Bake until cookies are browned around the edges but still slightly doughy looking in the centers.  Allow cookies to cool on the cookie sheet.  They will finish baking on the cookie sheet.  Once they are cooled, transfer them to a wire rack until they are completely cooled and set before stacking them or placing them in a container.
8. Store cookies in an airtight container with waxed paper between the layers.  Cookies should stay fresh for up to 3 days in an airtight container.