*12 oz is 1 and a half small containers of cool whip. With most recipes, measurements are critical, but for this one you have a lot of leeway with the amount of whipped cream that you use. Use one full 8 oz container and roughly 1/2 of the second. Also, this marshmallow filling is very sweet, so do a lot of taste testing and if it is too sweet, add up to the remaining 4 oz of cool whip.
**If you are going to add marshmallows on top or toast them, do it immediately before serving, as they get a bit stale and hard in the refrigerator.