To make caramel, place 2/3 cup sugar in a large, heavy-bottomed saucepan, add 4 tablespoons water, and bring to a boil over medium heat. Leave to caramelize, about 10-15 minutes. The caramel will reach a temperature of almost 180 degrees F, so care and attention are required. To caramelize sugar correctly, invest in a proper sugar thermometer. Do not leave the pan unattended when sugar is caramelizing.