Mom Tip: All honey hardens and crystallizes over time, but there’s no need to toss it. To bring honey back to its translucent, liquid state, just place the opened jar in a saucepan filled with about an inch of water and place over very low heat, stirring often, until the crystals melt. Alternatively, heat the opened jar in the microwave on high power in 10-second increments, stirring intermittently, until it has liquefied. Once cooled, use the honey or screw the lid back on for storage.
This tip from Cook’s Illustrated.