It was my favorite too , back in the early 70's when we were in the 'Friendly marketing area'.
I think it was made of the Milk Chocolate Cocoa Mix and some very thick sweeteners...The marshmellow creme you mentioned was a very good possibility. That topping over several scoops of Buttercrunch was high on my list of 'Must Haves'.
My daughter loved it on the Pistachio Ice Cream.
BTW Jozy, Welcome to the Roadfood Group!