Preheat the oven to 225ºF.
Place ¼ cup of sugar and the egg whites in the bowl of a stand mixer fitted with the whisk attachment. Mix on the lowest setting for 2 minutes.
Add another ¼ cup of sugar and increase the speed to medium, whisking for an additional minute.
Add the remaining sugar, cornstarch, cream of tartar, and vanilla. Whisk on medium-high until the mixture is smooth, thick, and silky white, forming stiff peaks.
Place the meringue on a baking tray lined with parchment paper or a baking mat. Using a spoon, gently create a well in the center, forming an 8-inch round meringue.
Bake in the oven for about 3 hours. Let the meringue cool completely in the oven.