Melt the Mars bars and butter or margarine in a large pot on low to medium heat on the stove, stiring to be sure it doesn’t burn to the bottom.
Add in the Rice Krispies and mix thoroughly to coat evenly. Transfer the mixture into a greased 9×9 pan, pressing down to pack.
Topping: Melt the chocolate chips and butter on low to medium heat in a sauce pan, stirring to ensure no burning to the pot. Pour the melted topping evenly over the top of the pressed Rice Krispies mixture.
Cool in the fridge before attempting to slice into squares.