Heat the oven to 250 degrees F. Line a half sheet pan with parchment paper. Use a 9-inch round plate and trace a circle in the middle of the parchment. Turn over the parchment.
Place the egg whites and pinch of salt in the bowl of a stand mixer and, using the whisk attachment on high, whisk until stiff peaks form, 4 to 5 minutes. Reduce the speed to medium and slowly add the sugar over 2 minutes. Stop and scrape down the sides of the bowl. Increase the speed to high and whisk until the mixture is smooth and glossy and stiff peaks form, 6 to 7 minutes. Decrease the speed to low and add the vanilla, vinegar, and cornstarch. Mix just to combine.
Gently spoon the meringue onto the parchment and spread to fit the shape of the circle, forming a slight well in the center. Place the meringue into the oven and bake for 45 minutes.
Turn off the heat and leave in the oven for 3 hours, or until the meringue is crisp and dry on the outside. Open the oven door and cool completely before removing from the oven, approximately 30 minutes.
Recipe courtesy Alton Brown, 2010