1. Preheat oven to 350 degrees Fahrenheit. Grease a 9×13 inch pan or line it with parchment paper that sticks up above the sides, which can be used to lift the finished brownies out of the pan and make cutting easier. Set pan aside.
2. Combine the butter and chocolate in a microwave safe bowl and heat in 20-30 second increments, stirring well after each, until melted and smooth.
3. Add the sugar and whisk until combined.
4. Add the eggs and vanilla extract and whisk together to combine.
5. Add the cocoa, flour and salt and stir with a rubber or wooden spatula until well combined. Batter will be very thick.
6. Stir in the chopped Oreos.
7. Spread the batter evenly into the prepared pan, then bake for 25-30 minutes. To test the brownies for being done, insert a toothpick into the center. If it comes out with just a few moist crumbs, they’re done.
8. Set the brownies aside to cool. When mostly cool, make the cookies and cream layer.
9. Add the white chocolate chips and heavy whipping cream to a large microwave safe bowl and heat in 20-30 second increments, stirring well after each, until melted and smooth. Mixture will be thick.
10. Stir in the powdered sugar and chopped Oreos, then spread evenly on top of the brownies. The mixture will be thick, just use your spatula to help spread it.
11. Allow the brownies to cool completely, then cut into squares. The cookies and cream layer will be quite firm to the touch, but great on top of the brownies.
12. Store the leftover brownies in an air tight container at room temperature for up to a week.