I killed my last blender trying to blend biscuits. And one time when I had a new mortar and pestle, I broke the biscuits that way (nb: not time efficient).

I think the trick is not to do too many at a time. I killed the last blender putting the whole packet in.

But yeah - a couple of ziplock bags (because I always break at least one bag corner) and a rolling pin or tin of something works well.