Preheat the oven to 350° degrees and line a 9x9 baking dish with parchment paper. (Leave the paper hanging off the sides so you can lift the brownies up.) Spray lightly with non-stick cooking spray.
In a large mixing bowl combine the flour, salt and cocoa powder, mix and set aside.
In a medium saucepan, add the butter, oil, and ½ cup sugar stirring until butter is melted. Remove from heat.
In a separate bowl, add the eggs and egg yolk, remaining 1 cup sugar, and whisk until everything is combined. Add in the vanilla extract.
Slowly add in the melted butter mixture and stir until just combined.
Add in the dry ingredient mixture and combine using a rubber spatula.
Fold in the chocolate chips and chopped Oreo pieces.
Pour brownie batter into the prepared pan and smooth in an even layer.
Add additional Oreo pieces if desired.
Bake in preheated oven for about 30 minutes, or until toothpick comes out clean when inserted in the center.
Remove from oven and allow to cool for a minimum of one hour before slicing brownies. Enjoy!
Notes
You can melt extra white chocolate chips in the microwave and add to a zip lock bag with the tip cut off and drizzle all over top of the sliced brownies for an extra step!