Preheat oven to 410° degrees F. Line 2 baking sheets with parchment paper; set aside.
In the bowl of a stand mixer, cream together the cubed cold butter and both sugars with the paddle attachment on low speed for 30 seconds. Increase speed to medium and continue beating for 30 seconds. Lastly, increase speed to medium-high and beat for an additional 30 seconds until light and fluffy. Scrape the bottom and sides of the bowl if needed.
Beat in the eggs, one at a time, followed by the vanilla extract. Lastly, add in the cake flour, oats, all-purpose flour, cornstarch, baking soda, salt, and ground cinnamon and mix on low speed until incorporated. Stir in the butterscotch chips. Chill the dough for 15 minutes.
Using a digital cooking scale for accuracy, measure out 6 oz of dough into a tall, rough and loosely packed dough ball. Place 4 dough balls staggered 3" apart onto a baking sheet. Bake one sheet at a time in the center rack of the oven for 11-14 minutes or until the cookies appear dull and dry in texture, are light golden brown and appear set. Cookies will be underbaked and gooey in the center as is signature of Levain style cookies but will continue to finish cooking as they cool on the baking sheets, so do not over bake! Cool on the baking sheets for at least 30 minutes as the cookies are quite fragile while they're hot. Keep remaining dough refrigerated while cookies bake.