A good rock candy recipe is available on Food.com. It takes 30 minutes to prepare, contains 243 calories per 100 grams and contains only water and granulated sugar.
To make Food.com's rock candy recipe, first pour 1 cup of water into a small saucepan. Pour 2 cups of granulated sugar into the water and heat the mixture on medium heat, stirring until the sugar completely melts. Keep adding sugar to the mixture until you see that no more will dissolve in the water. Remove the saucepan from the stove and let the mixture cool until it is slightly warm.
Pour the mixture into a glass jar, then tie one end of a heavy cord around the middle of a pencil. Place the pencil over the top of the jar and let the cord fall into the mixture. Crystals start forming after a few hours. Wait one day, then take the cord from the jar and pour the mixture back into the saucepan, reheat it and cool it. Pour the mixture back into the jar and put the cord with the crystals into it once again. More crystals eventually start forming. The candy should grow every day. When it has reached a preferable size, cut off the excess string before eating.