Combine the chocolate chips, peanut butter and butter in a large saucepan over medium-low heat, stirring constantly until completely melted and smooth.
Reduce the heat to low and add the marshmallows. Continue stirring until the marshmallows are all melted. Remove from the heat and stir in the vanilla extract and cereal, stirring to evenly coat. Immediately turn the mixture into the prepared pan, pressing it into an even layer.
Dust the top with powdered sugar and allow to set at room temperature, at least 30 minutes. Cut into bars and serve. Leftovers can be stored in an airtight container at room temperature or in the refrigerator for up to 5 days.