This is very annoying, but on international flights I'm able to partially fix it by putting the butter tub on my seat underneath my thigh while eating the appetizer. Usually, by the time I get to the salad after it, and want the buttered bread to accompany it, the butter is at least warm enough to be somewhat spreadable.

Yes, it's ridiculous that I have to sit on my butter just to do the thing butter is used for, but a J pax's gotta do what a J pax's gotta do.