Dissolve sugar in water over medium heat, in a medium saucepan. Increase heat to high and boil until syrup reaches 238 degrees F on candy thermometer. Whip egg whites and salt in a large bowl using a stand mixer or hand mixer on 4th speed until stiff peaks form. When syrup reaches 238 degrees F, reduce the mixer to the 3rd speed. Slowly add the hot syrup to egg mixture, carefully pouring it down the side of the mixing bowl. Continue mixing on 3rd speed until mixture reaches room temperature or put mixture in the refrigerator until cooled. Once cooled, whip mixture on 3rd speed and add butter in small pieces, beating until smooth, then beat in the vanilla extract.
This recipe was provided by professional chefs and has been scaled down from a bulk recipe provided by a restaurant. The Food Network Kitchens chefs have not tested this recipe, in the proportions indicated, and therefore, we cannot make any representation as to the results.