My Wilton instructor gave me the following recipe. I've never used it, as I discovered the mmf on this site and haven't looked back since. This recipe is supposed to work very well and should taste much better than that icky boxed stuff. This one is supposed to be made in the mixer, but I would try by hand if you prefer. Either way, it's going to be a sticky mess for a bit.
Grease dough hook on mixer very well with crisco. To 1 jar (not sure what size) marshmallow cream, add 3 cups icing sugar. Knead with dough hook and then continue by hand adding a bit of sugar at a time until fondant is of right consistency.
If you try it, let us know how it works.