Preheat oven to 400 degrees F for at least 15-20 minutes. Line two baking sheets with parchment paper.

In a large bowl of a stand mixer, beat the butter and sugars on medium-low speed until they start to come together, then increase the speed to medium-high for 4 minutes, stopping and scraping the bowl once partway through. It should be light and creamy.

Add the eggs and optional vanilla and beat again just until combined.

Add the all-purpose flour, cake flour, cornstarch, baking soda, and salt and pulse until the cookie dough starts to come together.

Add the chocolate chips and walnuts and mix again, just until the chips and nuts are evenly dispersed throughout the cookie dough.

Divide the dough into 8 large, rough mounds. Don't use a scoop or roll the dough into balls - the lumpy, bumpy signature look of these cookies is part of their charm. If you have a kitchen scale, each ball should weight approximately 6 ounces.

Space the cookies far enough apart on the baking sheet that they have some room to spread. I stick to 4 cookies per pan.

Bake for 10-14 minutes until lightly browned on the outside but still doughy and slightly underbaked in the centers. Let cool on the baking sheet for at least 15 minutes before removing or serving. The cookies will continue to set up and cook a bit from the residual heat during this time.

Store leftover cookies in an airtight container on the counter for up to 4 days.