Use frozen butter
If it is cheap butter, I always freeze some packages. Often it happened to me that I got them out of the freezer too late and could not reasonably spread buttered breads with them. A trick: chop off the required amount of butter with the cheese slicer. It is then spreadable and usable in no time.
Another tip that many may already know: If the butter is too hard for cake dough, you can plan it well on the cheese grater. It can then be used immediately.