2. Put remaining 2 cups sugar and 1/3 cup water into a large, heavy-bottomed saucepan, cover, and boil over medium-high heat until sugar dissolves, 4-5 minutes. Uncover and cook until sugar reaches 370º on a candy thermometer and turns dark reddish-brown, 15-20 minutes. Remove pan from heat and set bottom in a bowl of ice water for 1 minute. Add 1/2 cup water to caramel, return pan to medium heat, and stir until caramel liquefies, about 5 minutes.