Peanut Butter Cheerios Marshmallow Treats

Coat a 13x9-inch baking pan with cooking spray. Melt the butter in a large stockpot set over low heat. Once the butter has melted, add the marshmallows and cook, stirring, until the marshmallows have melted. Stir in the vanilla extract. Remove the mixture from the heat and stir in the peanut butter then stir in the Cheerios until they are well coated. Transfer the mixture to the prepared pan, pressing it firmly into an even layer. Allow the treats to cool to room temperature. Once the treats are completely cooled, melt the chocolate chips in the microwave or in a double-boiler. Transfer the melted chocolate to a sealable plastic bag then pipe it across the top of the treats. (Alternately, use a fork to splatter the chocolate across the top.) Allow the chocolate to cool then use a sharp knife to cut the treats into 12 squares. Serve immediately or store in an airtight container at room temperature.