Grab a small bowl, add a few ice cubes and add the butter soup to the ice directly. Stir it up a bit and the immediate chill will firm the butter back up to the point where you can use a spoon or spatula to get it back out of the bowl, all before the ice melts (and adds water to the mix).
When tested, the ATK team noted that the butter was just as good when used for baking. So the next time you leave the butter out just a little too long or decide to microwave it for just a few seconds, this tip may save the day.
How to Save Oversoftened Butter [America’s Test KItchen]