In 2-quart saucepan combine sugar, corn syrup, water and salt. Stirring constantly, bring to boil over medium heat. Without stirring, cook over low heat (small to medium bubbles breaking across surface of liquid) until temperature on candy thermometer reaches 260°F or small amount of mixture dropped into very cold water forms a hard ball which doesn’t flatten until pressed, about 40 minutes.
When temperature reaches 260°F, in large bowl with mixer at high speed, beat egg whites until stiff peaks form. Beating at high speed, gradually add hot syrup in a thin, steady stream. DO NOT SCRAPE SIDE OF SAUCEPAN. Continue beating at high speed until mixture begins to lose its gloss, about 3 minutes.
Reduce speed to low. Beat in vanilla. Continue beating at low speed until mixture holds a peak and does not spread when dropped from a spoon, about 8 minutes. (If mixture becomes too stiff for mixer, beat with wooden spoon.) Immediately stir in nuts.
Working quickly, drop mixture by teaspoonfuls and or via pipping bag onto waxed paper*. If desired, garnish with walnut pieces or candied cherries. Let stand until set. Store in tightly covered container.
* OR, spread in 8- or 9-inch square baking pan lined with square baking pan lined with plastic wrap. If desired, garnish with walnut pieces or candied cherries. Cool on wire rack. Cut into squares. Store in tightly covered container.