Generously grease an 8 x 8 baking pan with butter. Set aside.
Crush your chocolate sandwich cookies in a sealed zippered bag with a rolling pin (note: alternatively you can pulse in a food processor).
In a large pot, add marshmallows and butter (note: be sure to reserve 2 cups of marshmallows for mixing in at the end). Melt over medium-low heat, mixing constantly. Once marshmallows are melted, remove from heat.
Add vanilla extract and salt, stir.
Add puffed rice cereal, crushed chocolate sandwich cookies, and remaining marshmallows. Stir fairly quickly until all ingredients are evenly distributed and then transfer to your greased baking pan. Using a piece of plastic wrap that has been buttered, press the Oreo Rice Krispy Treats into your prepared pan.
Melt your white chocolate in a microwave safe container until 3/4 of chocolate is melted. Continue mixing your chocolate until all is melted. Pour melted chocolate over surface of Oreo Rice Krispie treats. Spread over Rice Krispie treats.
Sprinkle additional crushed Oreo pieces on top of melted chocolate layer.
Cool at room temperature until surface feels firm (~1 hour).
Cut into 12 to 16 pieces and enjoy!