Preheat the oven to 325°F.
Whisk the All-purpose flour, cake flour, cornstarch, baking soda, baking powder, and salt together in a large bowl. Set aside.
2 1/2 cups All Purpose Flour, 1 1/2 cups Cake Flour, 2 tsp. cornstarch, 1 tsp. baking soda, 1 tsp. baking powder, 1 tsp. salt
Place the butter and sugar into the bowl of a stand mixer and secure the paddle attachement. Turn the mixer on medium and cream the butter for 2-3 minutes until light and fluffy.
1 cup cold, unsalted butter (16 Tbsp.) cubed, 1 1/4 cup granulated sugar
Add in the eggs, egg yolks and cake batter extract and blend until mixed. If any of the butter gets stuck on the paddle attachment or sides of the bowl, use a rubber spatula to knock it off.
2 large eggs, 2 large egg yolks (no whites, just the yolks), 1 tsp. cake batter extract
Turn the mixture down to a slow setting and gradually add in the flour mixture. I add in about 1/4 cup at a time.
Add in 15 of the Oreos, white chocolate chips and sprinkles and mix just until combined. Turn the machine off.
25 Golden Oreos, divided, 1 cup white chocolate chips, 1/2 cup rainbow sprinkles
Spray a 9x13 inch baking dish with non-stick baking spray. Press dough evenly into the pan using clean hands or the back of a measuring cup.
Break up the remaining 10 Oreos and press onto the top of the dough.
Bake for 18-20 minutes, or until a toothpick inserted in the middle comes out with a few moist crumbs on it. Cookie bars will continue to cook in pan once you remove from the oven, so I recommend pulling them out before the edges begin to brown too much.
Cool bars completely before cutting into squares and enjoy!