Preheat oven to 200 degrees. Stir together 1 cup sugar and
the cornstarch in a small bowl. Beat together egg whites,
1 teaspoon lemon juice, and 1/4 teaspoon salt with a mixer
on low speed until very frothy. Increase speed to
medium-high and gradually add sugar mixture, beating until
stiff, glossy peaks form, 12 to 15 minutes, scraping down
sides of bowl halfway through.