Preheat your oven to 350°Fahrenheit. Line an 8x8 baking pan with parchment paper using metal binder clips to hold down the sides. Set aside.
In a microwave-safe bowl, melt the butter, and let it slightly cool. Using a whisk, add the light brown sugar and granulated sugar, whisking until well combined and smooth. The batter will start to grow in volume.
Add the egg and whisk vigorously for around 20 seconds, then add the egg yolk and repeat. Mix in the vanilla extract just until combined.
Using a rubber spatula, add the flour, baking soda, cornstarch, and salt. Gently fold until the dry ingredients are just combined.
Gently fold in the chopped Oreos and chocolate chips.
Pour the blondie batter into your prepared pan, spreading it evenly for a finished look. For extra appeal, sprinkle additional chocolate chips and chopped Oreo cookies on top.
Bake the Oreo blondies for 30-35 minutes, depending on your oven. Mine took 35 minutes. The blondies are ready when the edges are lightly golden, and a toothpick inserted in the center comes out with a few moist crumbs.
Let the blondies cool completely in the pan before cutting into squares and serving.