At the hard crack stage, your sugar syrup is between 300 and 310 degrees Fahrenheit. There's now almost no water left in the pan at all, and the mixture is thick, viscous, and a dark golden brown.

As for the sugar water, be very careful as you watch it get it to a rapid boil and use a large enough pot so there’s no overflow. Ideally, a candy thermometer or instant-read thermometer would ...