I'd like to share several tips on softening brown sugar when it hardens:
Place a lettuce leaf or slice of bread in the container, seal and allow to sit for a few days.
Place the brown sugar in the microwave just enough to soften.
Put a slice of apple in the brown sugar.
Try storing brown sugar in the freezer, in an airtight container. This helps prevent the sugar from hardening.
In a pinch, you can use a grater and grate off as much as you need for the recipe.
Do you have other brown sugar tips?