Baking: clumped brown sugar

Self-tutoring about baking situations: the tutor mentions reconditioning clumped brown sugar for use.

The other day, making apple crisp, I realized the only brown sugar available was in three large clumps, each around the volume of a large apple. Yet, I needed to powder them so I could measure the brown sugar in a cup. What to do?

I sliced each clump into strips, then broke them down with my fingers. This produced many, much smaller clumps. To get to powder, I took out a jar with a flat bottom and pressed and twisted down on those.