Your brown sugar gets too much air
THE RESULT: A hard heap.
THE FIX: When you find your brown sugar in a brick-like mound, blame improper storage—exposure to air causes the moisture in the sugar to evaporate. There are a couple of ways to restore softness. If you need the sugar immediately, place it in a microwave-safe container, cover with a damp (but not dripping) paper towel, and cook at HIGH in 30-second intervals until it’s softened. Microwave-softened sugar hardens as it cools, so only heat the amount you need. A longer method with more lasting results: Add an apple slice to the container, seal, and wait a day or so. The sugar will absorb the moisture from the apple. In the future, make sure you store brown sugar in an airtight container in a cool, dry place (but not in the refrigerator).