Preheat the oven to 275F. Line a baking sheet with parchment paper and draw a 6" circle. It doesn't have to be exact. Flip the parchment so the circle is underneath.
In the bowl of a stand mixer fitted with the whisk attachment, beat the egg whites on medium speed until frothy.
Beat in the cream of tartar.
Increase the mixer speed to medium-high and beat the whites to soft peaks.
Whisk together the sugar with the cornstarch.
While continuing to beat the egg whites, gradually add the sugar mixture (a couple tablespoons at a time) and beat until glossy and stiff peaks form.
Spoon the meringue onto the parchment circle. Use an offset spatula to spread the meringue evenly to the edges of the circle. Create design into the meringue (see my reels on Instagram)
Bake for 60 minutes or until the meringue starts to turn a very pale tan color.
Reduce the heat to 250°F (do not open the door) and continue to bake for 45 minutes.
Turn off the oven, (do not open the door) and turn on the light. Leave the meringue sitting in the cooling oven for hour, up to overnight. The center will collapse and you might see some cracks - totally normal.