Q: My brown sugar has turned rock-hard. What can I do to soften it without melting it?
A: There are a number of popular tricks for softening brown sugar. And that's a good thing -- since brown sugar is much moister than granulated sugar, it dries out easily.
If you have a couple of days, try placing a slice of apple and the hardened sugar in an airtight container. Check it after a day or so and see if the sugar is crumbly again.
If you're in a hurry, put the brown sugar in a dish covered by two damp paper towels and a lid. Microwave it on high (100 percent) power for 30 to 60 seconds, then break it up with a fork. Or put in an ovenproof dish, cover it with a damp cloth and put it in a 250-degree oven for a short time, no more than 10 minutes.
In both cases, check often to make sure the sugar isn't getting hot enough to melt.
Of course, the simplest solution is just to keep the sugar from hardening in the first place. I always double-bag brown sugar, keeping the bag it comes in sealed in a resealable freezer bag after opening.