In a large mixing bowl, combine the Captain Crunch cereal and powdered sugar.
In a saucepan over low heat, melt the butter and peanut butter together, stirring until smooth.
Remove from heat and pour the peanut butter mixture over the cereal. Stir until all the cereal is evenly coated.
Press the mixture firmly into a greased 9x13-inch baking dish.
In a microwave-safe bowl, melt the milk chocolate chips in 30-second intervals, stirring in between until smooth.
Pour the melted chocolate over the cereal mixture and spread evenly.
Sprinkle the Reese's Pieces on top, gently pressing them into the chocolate.
Refrigerate for at least 1 hour to set.
Once set, cut into bars and serve.