Place egg whites in the bowl of a large stand mixer; let stand at room temperature for 30 minutes. Meanwhile, line three 15x10x1-in. baking pans with waxed paper., In a heavy saucepan, combine the sugar, water and corn syrup; cook and stir until sugar is dissolved and mixture comes to a boil. Cook over medium heat, without stirring, until a candy thermometer reads 250° (hard-ball stage)., Just before the temperature is reached, beat egg whites until foamy. Gradually beat in gelatin. Beat until stiff peaks form. With mixer running on high speed, carefully pour hot syrup in a slow, steady stream into the bowl. Beat just until candy loses its gloss and holds its shape, about 5 minutes. Immediately stir in walnuts., Quickly drop by tablespoonfuls onto prepared pans. Let stand at room temperature overnight or until dry to the touch. Store in an airtight container at room temperature.