Microwave the brown sugar with a damp paper towel for 10 to 20 seconds
Place the brown sugar in a sealed container with a slice of bread overnight
Add a few apple slices to the container and seal it for several hours
Use a terra cotta brown sugar saver soaked in water and placed in the container
Break up the hardened sugar with a fork after softening
Warm the sealed container briefly in a low oven if the sugar is in an oven-safe container
Store brown sugar tightly sealed to prevent it from hardening again