In a large bowl, microwave the marshmallows and softened butter for 1-1:30 minutes or until the marshmallows are soft and butter is melted. Add the peanut butter and stir it into the melted marshmallow. Next, add the chocolate chips and rice crispy treats and stir all together. The chocolate chips will melt into the mixture. Move the mixture to your 9 x 13 dish. Now to make the chocolate topping: In a small bowl add 1 cup milk chocolate chips. Heat 1/4 cup milk in the microwave for 40 seconds then pour over the chocolate chips and let sit for about 1 minute or until the chocolate chips start to melt. Stir until a chocolate sauce forms. Pour over the top of the rice crispy treats in the dish and spread across the top. Chop up 6 Reese's peanut butter cups and sprinkle on top. Cool in the fridge until chocolate sets.