The directions on the side of my box say " to soften brown sugar that has hardened, place in oven-proof container and warm in 250F degree oven until sofr OR place in microwave container and heat on high, checking every 30 seconds. Measure desired amount. As sugar cools it will harden again."

I keep mine in a tupperware and put the whole thing in the microwave when I need some and it works like a charm.

Tracey