Combine sugar, corn syrup, salt and water in heavy saucepan. Cook and stir over medium-high heat until mixture starts to boil. Clip a candy thermometer to the side of the pan. Reduce heat to medium; continue cooking, without stirring, until the thermometer registers 260 degrees, hard-ball stage (10-15 minutes).
Meanwhile, in the mixing bowl of a stand mixer fitted with a whisk attachment, beat egg whites on medium high speed until stiff peaks form; set aside. (You want to reach stiff peaks as the sugar reaches hard ball stage).
When sugar mixture is ready, remove saucepan from heat and remove thermometer. Gradually pour hot mixture in a thin stream over egg whites, while beating on high speed for about 3 minutes, scraping down the sides of the bowl as necessary. Add vanilla and food coloring (if using). Continue beating on high speed until candy starts to lose its gloss and begins to thicken (4-6 minutes). When beaters are lifted, mixture should fall in a ribbon that mounds on itself.
Test mixture by dropping candy by a teaspoonful onto waxed paper. If it stays mounded, the mixture has been beaten sufficiently. If mixture flattens, beat 1/2 to 1 minute more. If mixture is too stiff to spoon, beat in a few drops of hot water until candy is a softer consistency.
Immediately stir in fruit and/or nuts if using. Quickly drop candy by the teaspoonful onto waxed paper sprayed with cooking spray. Cool completely before storing in a tightly covered container. Makes approximately 40 pieces
Cook's Note: The weather must be dry for the candy to dry, so if it's raining or very humid (over 50%) then consider making the candy on another day!