In 2-quart heavy saucepan, mix sugar and corn syrup; add candy thermometer. Cook over medium heat, stirring gently, until sugar is dissolved. If granules of sugar become stuck to sides of saucepan, use wet pastry brush to brush granules down towards syrup. Cook syrup, without stirring, until thermometer reads 310°F. If hot spots or darker areas occur while cooking, gently roll saucepan around to evenly disperse syrup.