In a small saucepan over medium-high heat, combine the sugar with the 2 tablespoons water. Bring to a boil and cook, stirring occasionally, until the mixture is syrupy and brown and has reached a temperature of 290ºF on a candy thermometer, for about 3 minutes. (Watch this closely and remove from the heat before it scorches.)
Quickly dip the pot into the ice water to bring down the temperature of the caramel. Remove from the ice water and immediately dip a whisk into the mixture and pull threads of the caramel over the ice cream. You must work quickly, or the mixture will harden in the saucepan. If it does, reheat it over medium heat, taking care not to let it scorch, and repeat the process. The candy will harden when it hits the ice cream.
Yield: enough for 4 servings of ice cream