Mix butter sugar eggs and vanilla. Add flour, cocoa and baking powder. Mix well and place in a 9×9 pan. Bake at 350 for 15-18 minutes. When done sprinkle with marshmallows and bake again for 3 minutes. Cool In a saucepan combine chocolate chips and peanut butter. Melt over low heat until smooth. Stir in cereal and spread over cooled bars. To cut them, I placed them in the fridge for about 20 minutes to set well.