Preheat oven to 400 degrees.

Line 2 baking sheets with parchment paper, set aside.

In the bowl of a stand mixer, combine cold butter, brown sugar and granulated sugar. Mix on medium speed for about 4-5 minutes or until creamy.

Add eggs, one at a time, beating after each addition.

Add vanilla.

In a separate bowl, combine the flour, cornstarch, baking soda and salt. Whisk to combine.

Add dry ingredients to butter/sugar mixture. Mix until almost combined.

Add chocolate chips and walnuts, mix until combined, but don't overmix.

Divide dough into 8 large clumps and place 4 on each baking sheet.

Bake at 400 degrees for 12-15 minutes, rotating pans half way through.

Remove from oven and let set for at least 10 minutes before moving to cooling rack to cool completely.