Line a 9x13-inch pan with foil or parchment and spray with nonstick cooking spray.

Measure out cereal and place in a large bowl.

Melt the butter in a large pot over medium low heat. Add the peanut butter and stir until combined.

Add the marshmallows and stir until melted. Remove from heat and stir in vanilla extract.

Add cereal and stir to coat with the marshmallow mixture. Immediately pour into prepared pan.

Press firmly to compact. Tip: spray wax paper with nonstick cooking spray so you can press without it sticking to your hands.

Let set until firm then slice into bars.