Combine 1/2 cup sugar, 3 tablespoons water, and the corn syrup in a saucepan, and clip a candy thermometer to side. Heat over medium heat, stirring occasionally, until sugar has dissolved. Raise heat, and bring to a boil (do not stir). Cook, washing down sides of pan occasionally with a wet pastry brush to prevent crystals from forming, until mixture reaches 230 degrees, 5 to 10 minutes.Advertisement
Meanwhile, beat egg whites on medium speed until soft peaks form. Gradually add remaining 4 teaspoons sugar, beating until incorporated. Remove syrup from heat. With mixer on medium-low speed, pour in syrup in a slow, steady stream down side of bowl (to avoid spattering). Beat on high speed until mixture has cooled, about 7 minutes (it should be thick and glossy). Use immediately.