I made mmf for the first time, and it was way to soft, didn't hold up or anything. How do I make it harder, but not so hard that I can't work with it?

have you let it set? i usually let my mmf set overnight to firm it up a bit. mmf can be quite finicky, a lot of it depends on the marshmallows and their freshness. if not you could always add a tiny bit of tylose or gumtex. hth!

I also make my mmf at least a day in advance. Curious what recipe you are using?

If it doesn't firm up enough resting overnight, next time you make it, add less water.