I do this:
Put open bag of sugar in the microwave with a cup of water next to it. Microwave on high for 2-3 minutes. Watch closely to avoid melting the sugar. If your microwave doesn't have a carousel, turn the bag after each minute.
Note: Unused sugar will dry up again. But the process can be repeated each time you need the sugar until its used up.
Lots of other methods here:
http://tipnut.com/10-ways-to-soften-hard-brown-sugar/
Put open bag of sugar in the microwave with a cup of water next to it. Microwave on high for 2-3 minutes. Watch closely to avoid melting the sugar. If your microwave doesn't have a carousel, turn the bag after each minute.
Note: Unused sugar will dry up again. But the process can be repeated each time you need the sugar until its used up.
Lots of other methods here:
http://tipnut.com/10-ways-to-soften-hard-brown-sugar/