In a large saucepan, add in the marshmallows and butter. Over medium heat, stir the marshmallow mixture until it's completely melted and there are no lumps.
Add in the crushed cookies and rice crispies. Stir until everything is evenly covered with the marshmallow mixture.
Pour the rice crispy treats into an 11x7 pan. I sprayed nonstick cooking spray in my pan, but I don't think it's necessary.
Placing a piece of wax paper or parchment paper over top of the mixture, press the rice crispy treats into the pan. Don't press real hard, if you want a tender rice crispy treat. If you want a firmer rice crispy treat, press with all you've got!
Let cool and cut into squares.
Microwave the white chocolate melting wafers in the microwave for 30 second intervals until completely melted. Using a spoon, flick the white chocolate across the cut squares of rice crispy treats. Let cool, and serve!