Lightly grease a 9-inch x 13-inch pan and set aside.
In a large pan, melt the butter over medium heat. Add the marshmallows and stir constantly until melted. Remove from the heat, add the peanut butter and stir well. Add the cereal and stir until well combined. Carefully press into the pan with wax paper or buttered fingers.
Mix together the chocolate chips and 1 1/2 tablespoons peanut butter and melt (easiest in the microwave, stirring every 30 seconds until melted). Spread the chocolate over the crisped rice treats. Let sit until the chocolate is set. Cut and serve.