Dark brown sugar adds depth to so many dishes. Of course, it's wonderful in many baked goods. It also adds a lot to some vegetable dishes. To keep it soft, after opening a package, I slip in a chunk of fresh potato and just try to keep the package folded up well. I leave it in the refrigerator. There's one thing you have to remember about this method for maintaining the softness. After a while, maybe a few weeks, you have to take a very thin slice off the potato so that it doesn't become black and unsightly, or simply replace the potato chunk every few weeks.