Brown sugar is delicious and a staple of many baking recipes. Nothing is more frustrating than finding your ingredient has turn hard since you last used it. First of all, transfer the brown sugar into a zip-lock bag upon opening the first time. This way you can actually place your measuring cup inside the bag to get the right amount you need. Toss a few mini marshmallow in the bag and seal to keep fresh. Keeping the bag in the freezer will help it last longer too.