Immediately spread into prepared pan. Fudge sets quickly!
Update 12.14.19: I had a reader who wrote in that she planned to make mini muffin cups of fudge (love this idea!!), and the fudge was setting a bit too fast. I think this could probably be done if you act super quickly and know ahead of time that it's fast-setting. Now I've updated the notes, so hopefully that info helps someone else if they have a similar idea!