So I made Black MMF yesterday for a cake, but when I checked it this morning, it was very firm and stiff and hard. Can anyone tell me why?
I actually just had that happen to me with a regular batch of MMF. I think I added my confectioners sugar too fast and it seized up. It was okay while I was kneading it but the next day I couldn't even squeeze it because it had gotten so stiff. So- either I measured wrong and put in too much or I added it too fast.
You can try kneading in some shortening and see if that helps. Or pop it in the microwave for 20--30 secs and that will soften it a bit. But be careful...sometimes it gets hot spots.