Preheat the oven to 350 degrees Fahrenheit. Line a 9x13-inch aluminum pan with parchment paper or spray with cooking spray. Set aside.
In a large mixing bowl or stand mixer, cream together butter and sugars until smooth and fluffy- around 3-5 minutes.
Add in the egg and vanilla and mix until combined.
Stir in the pumpkin puree.
In a medium bowl, whisk together flour, baking soda, salt, pumpkin pie spice, and cornstarch. Add the dry ingredients to the wet ingredients and mix until just combined.
Gently stir in the chocolate chips and Oreos (reserve a few for the top).
Spread evenly into the pan. Sprinkle the top with a few chocolate chips and Oreo pieces.
Bake for 23-27 minutes or until the center is cooked through. The edges will start to pull away from the sides and become golden brown.
Allow to cool completely before cutting and serving. Enjoy!