Boil water in a clean pot
Add white sugar gradually and stir until no more sugar dissolves
Remove from heat and let the syrup cool slightly
Pour the syrup into a clean glass jar
Tie a string or wooden skewer to a pencil and suspend it in the jar without touching the bottom
Cover the jar loosely with a cloth or paper towel
Leave the jar undisturbed in a cool, dry place
Wait several days to several weeks for crystals to form
Remove the rock sugar crystals from the jar
Let the crystals dry completely before storing
Store in an airtight container