1Cook sugar, corn syrup and water (use 1 tablespoon less water on humid days) in 2-quart saucepan over low heat, stirring constantly, until sugar is dissolved. Continue cooking, without stirring, to 260ºF on candy thermometer or until small amount of mixture dropped into very cold water forms a hard ball that holds its shape but is pliable.
2Beat egg whites in medium bowl with electric mixer on high speed until stiff peaks form. Continue beating while pouring hot syrup in a thin stream into egg whites, beating constantly on medium speed. (For best results, use electric stand mixer, not a portable handheld mixer since beating time is about 10 minutes and mixture is thick.) Add vanilla. Beat until mixture holds its shape and becomes slightly dull. (Mixture may become too stiff for mixer.) Gently stir in nuts.
3Drop mixture from buttered spoon onto waxed paper. Let stand at room temperature at least 12 hours, turning candies over once, until candies feel firm. Store in airtight container.