This Surprising Dessert Will Keep Brown Sugar Soft
Any home baker that has had to store brown sugar for a while, knows that it can turn into something resembling a sweet-smelling brick. That's largely because brown sugar has molasses in it, and over time, the water in the molasses will evaporate out causing the sugar to become hard (via All Recipes). When brown sugar gets so hard it cannot be easily broken through, it is all but impossible to get an accurate measurement for a recipe. Fortunately, if you store your brown sugar correctly you can avoid this issue.
Whether you need to soften up brown sugar after storing it improperly, or you are looking to properly store a new bag of brown sugar, you can use one dessert staple to accomplish both tasks in one go. All you need is a regular-sized marshmallow or two (via Eat This, Not That!). Marshmallows have a surprising amount of moisture inside of them, which they impart to the brown sugar when placed together in an air-tight container.
You can try these solutions too
If you don't have marshmallows on hand or you would prefer to use something else because you follow a vegan diet and don't want to buy the gelatin-based product, there are other ingredients you can use. According to Food52, a slice of white bread or even diced apple can be substituted in for marshmallows. The key is that these ingredients have a lot of moisture on their own and give off moisture that the brown sugar absorbs.
Another option that Food52 suggests is using earthenware containers such as their terra-cotta brown sugar saver. Like the other foods that lend moisture to brown sugar, earthenware easily absorbs and releases moisture that makes it a great storage material for brown sugar. However you plan to start keeping your brown sugar stored, now that you have these hacks under your belt, chances are baking with the rich ingredient will become a lot easier.