- Preheat oven to 350°F. 
- Line an 8x8 inch pan with parchment paper or non-stick baking spray and set aside.  
- Whisk together the dry ingredients in a large bowl: All-Purpose flour, cake flour, corn starch, baking soda, baking powder and salt. Set aside. - 1 1/4 cup All-purpose flour, 3/4 cup cake flour, 1 tsp. cornstarch, 1/2 tsp. baking soda, 1/2 tsp. baking powder, 1/2 tsp. salt 
- Using a stand mixer fitted with the paddle attachment, cream the butter, white sugar and brown sugar together up to 4 minutes or until light and fluffy. - 1/2 cup unsalted butter, cold, cut into cubes (8 Tbsp.), 1/4 cup granulated sugar, 1/2 cup brown sugar, packed (light or dark) 
- Add in the eggs, egg yolks, and vanilla extract.  - 1 large egg, 1 large egg yolk, 1 tsp. vanilla extract 
- Gradually add in the dry ingredients and then add in the Oreo cookies, mini chocolate chips and chopped cookies and creme bars. - 15 Oreos, divided (10 get mixed into batter, 5 go on top), 1/2 cup mini chocolate chips*, 4 (1.55 oz.)  HERSHEY’S Cookies ‘n’ Crème Bars , chopped* 
- Press dough into a prepared pan in an even layer. 
- Press more Oreo pieces on top and bake for ~20 minutes* or until a toothpick inserted into the center comes out mostly clean. 
- Let bars cool for ~15 minutes. Cut into bars and enjoy!