in large pot, 8qts is good. on high heat melt your butter, then add your marshmellos, stiring constantly. once all is melted and at a low boil, reduce heat to low and slowly add cereal. coating all the cereal well. remember to reserve 2 cups for your topping.
pour all into a slightly buttered 13x9 glass or metal baking dish. with a buttered flat bottom glass press the cereal to the edges of the pan. set aside.
in a medium sauce pan on high heat,melt your butter and melt 6 of the 12 squares. this will look like curdled cream once melted. with a wire wisk, whip butter and bark till smooth, wisk in your cream very fast this will create a smooth custard looking sauce. slowly add your mini marshmellos and continue to wisk fast till all is melted and smooth. you will have a light sheen to this mixture. pour at once over the treats spreading to the edges.
with a slight shaking of the pan even out the chocolate sauce till all is covered evenly. sprinkly the 2 cups of cereal that you set aside covering all the edges and center,press down slightly. let cool completely in fridge and cut into squares.