Place egg whites in a large stand mixer bowl; let stand at room temperature for 30 minutes. Meanwhile, line three 15x10x1-in. pans with waxed paper; set aside.
In a heavy saucepan, combine 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 260° (hard-ball stage). Just before the temperature is reached, beat egg whites on medium speed until stiff peaks form.
Slowly pour hot sugar mixture in a thin stream over egg whites, beating constantly. Add vanilla. Beat until candy loses its gloss and holds its shape, about 5-6 minutes. Immediately stir in crushed candies and food coloring if desired. (Do not overmix, or candy will get stiff and crumbly.)
Quickly drop by heaping tablespoonfuls onto prepared pans. Let stand at room temperature overnight or until dry to the touch. Store in an airtight container at room temperature.
Editor’s Note: We recommend making this candy on a clear day with low humidity.