Spray a 9 x 13'' pan with non-stick spray. Set aside
Put peanut butter, chocolate and butter in a large saucepan over medium heat. Melt together, stirring frequently. Add marshmallows and heat until they melt into the mixture, stirring frequently.
Pour Rice Krispies into a large mixing bowl. Pour peanut butter and chocolate mixture over cereal. Mix until combined.
Spread mixture into prepared pan and smooth out.
Refrigerate 2-3 hours or until firm.
Store in an airtight container in a cool place or in refrigerator for 2-3 days.
