Spray a 9 x 13 inch pan with nonstick cooking spray and set aside.
In a large saucepan, melt your butter, mini marshmallows and vanilla until just melted. Careful not to over cook.
Remove from heat once melted and add the frosting.
Stir until well combined.
Pour in the Rice Krispies and immediately stir and fold making sure the cereal is evenly covered. Be sure to scrape the bottom of the pot and fold it on top to ensure full and even coverage of the cereal.
Pour the mixture into the pan and press it in with your hands or rubber spatula.