I use brown sugar in my coffee every morning, and occasionally I forget to close up the plastic bag and it gets hard as a rock.
If this happens to you too, instead of chipping away at it to try to get a spoonful, simply place a piece of sliced bread in the bag and close it up.
The next day, the brown sugar will be nice and moist, and the bread will be hard as a rock.
I actually considered making one of my wacky videos to show you how it works in time lapse, but then I figured that would be about as interesting as... well, watching bread go stale.
Here are a few other ideas for softening brown sugar if you need it done in a hurry.