Preheat the oven to 350°F. Place chopped walnuts on a baking sheet and toast in the oven for 5- 8 minutes. Shaking the pan occasionally. Watch them closely to prevent burning. Set aside to cool.
In a medium bowl, whisk together the flour, cornstarch, baking soda, and salt and set aside.
In a stand mixer, cream together the butter and both sugars on a low speed until combined. Scrape the bowl down once or twice as needed. Add the egg and vanilla and beat until combined. Scrape the bowl down as needed.
Add the dry ingredients to the wet and mix on low until just combined. Add the walnuts and chocolate chips. Mix on low until combined. It should just take a few seconds.
Use a large cookie scoop to portion the dough onto a tray or baking sheet lined with wax paper. Then top each scoop with extra chocolate chips and walnuts.
Place the trays in the freezer for at least one hour. Transfer the frozen cookie dough balls to a freezer bag or airtight container. Freeze for at least 4 hours, but preferably overnight.
When you are ready to bake, preheat the oven to 325°F. Place frozen cookie dough balls on a baking sheet lined with a silicone baking mat or parchment paper. Bake for 21- 23 minutes or until lightly golden brown.
Let them cool on the baking sheet for 5- 10 minutes before transferring them to a cooling rack.